I would have, as well, but this is government housing, and I will have to pay for the damage. Still, I would like to have used Liquid Plumb-R on it LONG before now!
I used a quart of vinegar and a box of baking soda (this time) and a plunger in between applications. But what it did, apparently, was to loosen up all the gunk of all the previous tenants and clog up the drain beyond the traps.
Otherwise, only one sink would be clogged.
Yeah, they’re gonna have to snake it.