I think waiting is a smart move. Let your current dogs get settled (sometimes it can take a year, so the longer you wait, the better). I think this is especially important for your sister's dog. Poor thing is in a whole new place. Luckily his mommy is still with him, but it's still a new switch.
To be honest, if this was me, I wouldn't get a new dog until I had my own place. I don't know how it is there, but here some apartment complexes only allow 1 pet or 1 dog. Let her get established (working) and then consider bringing in a new baby.
As for you getting a little girl, do you guys want the girls to be the same age? Because you can go ahead and get one after a couple of months. It is your place.
