Good evening!
My problem is this. When I flush the upstairs toilet or drain the upstairs tub, the toilet downstairs in the half bath bubbles, and most recently has begun to overflow and then sucks the water out of the bowl and gurgles. I am wondering if the problem maybe a clogged vent pipe on the roof? Please can anyone offer any suggestions

One post's plenty. No need to double post if you're not answered right away
I am wondering if the problem maybe a clogged vent pipe on the roof?
That's where I would start. At the downstairs lavatory roof vent. This vent may be revented back in the attic to a existing roof vent so be sure and check that you're snaking the correct vent. Put out enough cable to reach the base and 25 feet more to clear the branch. Good luck, Tom

Thank you very much for your suggestion. I will do this and advise of the outcome.