Once they are living in your attic squirrels will investigate to see what they can find and often crawl into the walls.
Squirrels in my walls and ceiling.
But squirrels can get almost anywhere in the architecture of a house the eaves the walls and the ceiling the gap between the 1st and 2nd floor for example or a drop ceiling or a ceiling with a flat roof and no attic gap etc.
Seal them off with metal mesh to prevent the squirrels from making their way back in.
Above all check every inch of the walls and ceiling for potential access holes.
Will squirrels chew through the ceiling or wall squirrels will chew through virtually anything they see.
The principles for how to get squirrels out of your walls or how to get squirrels out of your house anywhere from the soffits to the eaves or ceiling are the same as for the attic.
Find the entry points make sure the young are removed fix all secondary entry areas mount traps on the main hole repair damages.
It is imperative for them to chew in order to grind down their constantly growing teeth.