West end of house has 6 drains into common drain line on west end of house. Have had whole line snaked twice in 2 weeks to the junction of main line exiting house to city sewer line. Could a clogged vent stack be the problem? There are 2 stacks, one around bath sink and other around kitchen sink. Clothes washer is furthest end & clean-out for this half of whole system. A large tree too close to the house may cause vent to be clogged. House was vacant for 2+ years before purchase, but was nicely remodeled. Attention to small details is very evident though.

could a clogged vent stack be the problem?
No a blocked vent will cause traps to be siphon dry but will not prevent drainage. You have a blocked or partially blocked drain. What size snake was used. Snake again, and again until drain is clear. Not sure where the tree is. If it is close to the drain you could have roots in the drain pipe but the tree will not block the vent.

Not sure if you are saying you snaked to where the main drain exits the house or to the street. Snake to the street.