240v Shared Service

Assuming USA (you didn't say where you are)

Just use an extension cord with two outlets, as you would with any other outlet. Stores often stock these extension cords next to the generators. Your circuit breaker will ensure that you don't overload your circuit, even if you should happen to use both devices at once.

Check with your local inspector, but some codes require each 240 to be on a separate breaker.

Not at the same time. If you AHJ allows it you could install a 30amp manual transfer switch so you could have two receptacles and switch the source back and forth as needed.