My upstairs bath tub leaks into my bath tub downstairs.. It comes up the drain weither it's the shower on or bath tub.

The ceiling of the downstairs bath is already shot so pull it down. Once the ceiling is down you will have a better view of the issue. From what you say it could be the drain. Fill a few buckets of water and pour them into the tub with the stopper open. Does it drip downstairs?

Yes it does. It is not leaking from the ceiling though it is coming back up the bath tub drain, as soon as you turn the water on upstairs it starts coming up the drain in the tub downstairs.

Does it come up through the lower drain if you dump buckets of water into the upstairs tub? If so you have a simple drain clog after the trap on the lower tub.

Yes it does. So do you think snaking the upstairs tub fix it?

No, your problem is below/ after the downstairs tub. Can you see the drain of this lower tub from the basement or crawl space? The drain between the vtwo tubs is clear,that why water from upstairs easily gets downstairs. Both tubs share the same branch drain line anditnisbthat line that needs snaking. Can you reach and open up the trap below the lower tub?