Potential free relays

Is it possible to connect two potential free relays output to one 240V supply and return?

not without a load.

Done all the time with single phase loads such as heaters.
BUT
As the "other" Dan said you must have a load or you will have short circuit.

Dan Bentler

You should check the specifications of the output relay for maximum current and voltage. Also be aware if you're switching an inductive load like motor or heavy duty contactor. The induced current when breaking such a circuit will eventually burn and/or weld your output relay contacts.