Don't want to be over capacity however don't want to get screwed either

[sunnydays]

I think you are doing the right thing. You cannot leave yourself in a bad position because of honouring commitments. I don't think the parents would pass up a good opportunity because they feel loyal to you either. You mentioned that the two part-timers are friends though...in that case I would be inclined to talk to Alice's mom now before she hears it from the other mom and feels like you are pulling the wool over her eyes.