Hello,
I've had my sink, and tub, & basement drain all come back up when my washer is running. I've put chemicals down all drains, fiancé has tried a plunger, I've even doing the old trick of baking soda & vinegar & salt. No results. Can you suggest any other ways to maybe help unclog it?

Locate the house clean outside and open it up. Is there standing water in the clean out? If there is you have a blockage between the cleanout and the street that must be snaked. Let me know what you find. Regards, Tom