If I wanted to go and get another bank account somewhere, could I if there is already a legal order on my current joint bank account?

Also, if my joint bank acct that has the legal order on it is now overdrawn, if I deposit more funds will those funds be applied to the overdrawn amount or does the company who put a legal order on the funds get them?

You can open another account, at a DIFFERENT bank, but they may find that too.

If the levy didn't satisfy the judgement, then it would depend on the wording of the writ. It may cover additional deposits too.