Can you have 3 pets in battle together???

Or do you have to  subitite one pets for another???

i like the idea of having 3 pets in 1 go.

one at a time, but you can switch in mid battle

once pets are release , they cannot be sealed?
so you have to choose your pets carefully?
and also you cannot put your pet in somewhere like pokemon center???
Coz i think i want to collect all the pets.