A: I don't know. I would hesitate doing it over the possibility one exhaust could be back pressured to the other bathroom.
A: It is not intended for that use.
A: Should be. Although there is a difference between 4” dust collection fittings, 4” pvc, and other 4” ducting. But it can be made to work.
A: No, I had to order - delivered to my store for free.
A: Not typically.