My daughter's hamster, Sneakers, passed away

He was 3.5 years old so we can't complain about his lifespan any...he had a great life and died while sleeping in nice clean warm bedding...nevertheless a sad day it was :/
Today I brought home two female
fancy mice and one female gerbil for her. All three are still pretty young...
The gerbil will receive Sneaker's old home and the mice will live in a brand new cage I purchased for them while picking them out...
I'm pretty sure we cannot connect the two cages together because they may not get along? But can they spend time "playing" together? She used to let Sneakers cruise around in Lincoln Log mazes etc and I'm sure she'll want to pull these three new ladies out to exercise and play and learn tricks like she did with the hamster but I'm not sure if she must work with the mice separately from the gerbil or can she work with all three together?
Thanks for any assist!