I would imagine you should. replenish nutrients and get the plant used to a bonsai conatiner/soil. that is, unless you want to grow the trunks thicker. than, keep them in a bigger container.

Depends on the particular species you have.

Josh

..... agree with Josh - varies by genus/species ...... especially in consideration of your zone. Few trees are appropriately repotted in August, no matter where you live, though tropicals will still do quite well in the southern half of the US.

Al