What’s a professional way to tell a job (Costco) how would you balance both of your 2 jobs between us? Need help with that question?

Answer 1

With your own story - and understanding they won't care since your balancing two jobs is your problem, not theirs.  They'll probably be flexible now since labor is short.  When they can do better they'll go with that instead. 

Answer 2

If you want the job... you don't ask this question.