And the panic starts setting in!
1) I have separate water bowls (actually I have 3 in the house & 2 outside, plus the kiddie pool that they both think is the best water bowl ever) but both dogs drink from any of the bowls.
2) Due to Tess' allergies, I'm feeding different foods.
3) I use separate food bowls. You may find one, the other, or both gets "growly" if the other approaches their bowl. Mine are fine but if I let him, Cody would eat all of Tess' food also. I feed at the same time but I always put Cody's food down first since he's alpha (most of the time). Frequently, even though her food is down, Tess will wait until Cody has completed his meal before she eats.
4) When giving bully sticks/bones/etc. I will frequently put down 3 (read somewhere that was a good idea) although it doesn't matter - they both want the same one and will take turns with it. The other 2 just sit there.
4) I have one large toy box for both. I consider some toys hers & some his, but they don't. Tess rarely plays with toys and frequently only if Cody brings one to her (she has him trained very nicely!)
5) I use two separate 6' leashes. Since I haven't done the best job teaching them to heel it gets a little dicey at times as they cross in front/behind me - but I've gotten very good at moving leashes from hand to hand. The rescue organization suggested a twinned lead so Tess was forced to keep up but I haven't tried it.
6) I walk both dogs at the same time - the first month was rough since Cody is a puller and Tess was a dragger (I was a sight to see with my arms stretched out as far as they could go) but we've worked things out and do pretty well. Frequently they now walk leaning against each other (I suspect trying to push the other off the sidewalk).
7) I'm trying to be more diligent in my training of two, which I do separately (drives the other one nuts!) When I first got Tess, I was trying to clicker train them at the same time and Cody lost ground since he wasn't getting the proper reinforcement since I was talking to Tess (he just didn't know that). As part of the training, I'm taking each on separate walks to work on their individual "issues"
8) I have separate beds/car seats/crates for each, but once Tess would rather snuggle up with Cody than lay in her own bed.
9) When I bathe them, I always bathe Cody first because Tess just lays at my feet waiting her turn.
I think the best you can do is just be flexible and patient...give something a try, if it doesn't work, try something else. I think a lot of things Mugsy and Kaylie will work out themselves - no matter what you have in mind.
Relax...you, Mugsy and Kaylie will do just fine!