What you might try. More than two hands helpful. Stoppers and water in all sinks and shower. Use plumbers helper/plunger at each drain to force water thru drain pipes. If air or water comes out of drains - add more standing water or have helper hold drain plug in place.
The shower probably has a HepVo
https://www.amazon.com/HEPVO-BV1BUB1...keywords=hepvo waterless trap. Using a snake would likely destroy it.
Every couple months I go thru the above routine as preventive maintenance.
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