2 ropes off of 1 anchor?

Long story short, my kids (both 8) have taken to climbing and I would like to climb with them.  My current weight prevent my wife from being able to belay me.  There is not a lot of places to climb by us and closest place is small and busy.  With that, I think it would be inconsiderate to set up to separate top ropes, especially since one would be for top rope solo and a lot of my time is spent belaying.  So here is my tentative plan.

Set up one top rope anchor.  Off that anchor is 2 carabiners with a rope fixed to them for the top rop solo.  Off of these 2 carabiners would also be 2 short slings to 2 more carabiners which would have the rope for the standard top rope set up.  My reasoning for the 2 sets of carabiners is to not have the standard top rope rubbing on the fixed rope.  While I see having an extra rope in the way for who ever is climbing being a pain, i think we could pull it off to the side to alleviate some of the inconvenience.

So, am I going to die?  Is there a better way to do this?  Or is it just overall a bad plan?

You could look into weighing your wife down when she's belaying you with nearby rocks/trees or bring a sandbag. If you're only top roping it should be fine. If you're looking to lead buy an Ohm

Will your idea work? Probably. Instead of running the extension slings off of the carabineer holding the fixed rope, I'd probably use the master point of your anchor. If you take care to pay close attention to what rope you are using for what purpose, it can be done safely. There will always be unused rope in the way of the climber. 

Is there a simpler way? What if you use a rope that is ~4x the length of your intended route and set it up as a TR. When you want to solo, you can set up a carabineer block (clove or butterfly a biner at the mid point of a rope, clip the "climbing" strand through the biner, then pull it until a fixed loop forms a noose around the TR biners) and fix the rope from the bottom. Be careful: you only TR solo from the strand that is fixed, the other end will not be fixed (use this strand to pull your biner block back down to reset the rope to normal TR duty). Since you're pulling that strand through 2 progress capture devices, clip a pack to the bottom of the climbing strand. Let's call this option 2.

Option 2 pros:
Simple anchor
One rope
Easy to swap between modes
Approach requires packing less gear (more room for kid supplies)... Depending on rope length. 

Option 2 cons:
Rigging and safety checks required between modes.
In TR solo mode, only one strand is fixed (primary and backup have to be on same strand)

Both options require a certain amount of careful evaluation for safety and rigging double-checks,but that can be said for all climbing activities. Because you initially suggested TR solo, I'm assuming you are comfortable safety checking yourself and that you understand the basic mechanics of this system.

Option 3: if the area is bolted for climbing on lead, put an Edelrid Ohm on the first bolt to the belayer's strand and TR with your wife belaying. No need for TR soloing. Belayer stands close to the wall when the kids climb to defeat the friction addition from the ohm. I use this when my wife belays me on lead, and I have ~75 lb on her. Your wife needs to stand 7-8 feet laterally from the bolt where the ohm is clipped for it to add the friction you desire. 

https://www.edelrid.de/en/sports/ohm/ohm.html

I apologize for the following:
I broke MP rules and gave you detailed advice instead of the accepted practice of telling you that if you are asking advice on this website, you clearly aren't qualified to leave your house. 
Someone is about to tell you my advice is dangerous and your entire family is going to die because I'm stupid.

Have fun, be safe, test your systems before any lives are on the line. 

Bo London wrote: Will your idea work? Probably. Instead of running the extension slings off of the carabineer holding the fixed rope, I'd probably use the master point of your anchor. If you take care to pay close attention to what rope you are using for what purpose, it can be done safely. There will always be unused rope in the way of the climber.

Is there a simpler way?  

There's a simpler way to do what you're recommending.  You can do it without needing a ton of rope.  

Set up your standard TR system.  When you want to transition to TR solo, take both strands that are hanging and tie them together with a BHK.  You've now created a loop or rope running through your anchor.  Clip a locking carabiner to the BHK and one strand to create a carabiner block.  Pull it up to the top, do your TR solo, rap the fixed side or clean the anchor.  If you rapped the fixed line, pull down the knot and you're back to a standard TR.

edit: added some clarity about the carabiner block.  

Just set two independent master points from the same anchor pro spaced about a foot apart.  
Or you can Kill two birds with one rope and have each of you simul-climb on both strands of the top rope.
At least pretty sure you’ll be able to kill two of something with this technique.  I’d stick with two master points.  That way you can climb with your kids and offer help and encouragement along the way.  

If that’s unnecessary, then the biner block option 2 above as Bo suggested is most efficient.   Not quite sure what Adam is suggesting with the BHK. At face value his extra locking biner seems superfluous and adds nothing unless you clove hitch it or use a butterfly or other knot to secure it to one strand and clip the other strand through it.  Maybe he meant this.

Thanks for thg he suggestions so far.  I will test some of this out at our wall at home and will likely have more questions after that.

+1 for anchoring the or weighting down the wife. This sounds like a fair amount of work/faff/hassle for a marginal benefit.

If there aren't any convenient trees/roots/boulders to sling, an ikea bag full of rocks makes for an easy ground anchor/weight that's relatively durable and cheap. 

Got a chance to play around with this at home today.  Here's what I did:

Used my smallest locking carabiners off my master point.  Tied my rope ends together and tied stopper knots in the tail ends.  Clove hitched my largest carabiner just above the knot, pulled it up to the master point and climbed.  Everything seemed to worked well.

In a crag climbing situation I will at a minimum fix the non climbing strand at the base of the climb and either weight or tie off my climbing side to make the start of the climb feed easier.  I also need a larger carabiner for the block.  

I will also be looking into getting my wife to belay me when she is climbing with us.  Will start by adding some weight to a pack and look for more information on anchoring her.  While anchoring seems to be popular, I'm have a bit of a hard time parsing through all of the conflicting information out there.

Thanks again to those who replied.

You have a few directions going on here, however to give one more on your original question.

Yes, I have set a fixed line and a TR off the same anchor before. Why? Because I like to take photos and jug lines sometimes while a friend is climbing a route. The hardest part is actually keeping the fixed line out of the climbers path. If the anchor is bomb proof its of no worries to me. To keep it clean I do keep a foot or so of space between the fixed line master and the TR master, just as you thought one should. This works if your both on the wall at the same time; climbing, jugging, taking photos, etc.

If you were not looking to have your kids TR at the same time you are TR rope soloing this sure seems like a lot of extra work for what could easily be solved with a bottom anchor on the belayer. Especially given that forces on TR falls are working in your favor of being far reduced compared to a lead fall or something of higher pulls.

 

An instructor at a class I took once suggested one of these for such a scenario (I am also a bigger guy). I'm not sure if this is for lead only or can be used for TR...so there's that. edelrid.de/en/sports/ohm/oh…

Another suggestion, if it's possible, set the trs on one route and TR on one next to it? You climb while the wife belays the kids. Come down, belay the wife and/or she can trs while you belay the kids. Switch routes when you're ready. This might only work if its relatively empty that day though 

The Ohm can be used for TR as well as lead.

My troll meter is beeping, but in case this is for real...

You're overthinking this. It sounds as though you're climbing beginner-level stuff so your kids will grow and have fun. So just use a Grigri to TR solo. It's a pain, but the routes you're likely climbing probably provide plenty of opportunities to pull slack. Save the more complicated systems for when you really do go out alone.