solenoids interfacing

For a pneumatic double solenoid valve, shall I use a relay for each valve separately, or a single relay could interface the two solenoids

If the two valves are operated with one relay, one valve will always be open. Relay ON drives the cylinder to one extreme...relay OFF drives the cylinder to the other extreme...no stop position with both valves closed. If that's what you want, one will work. Otherwise you will need two relays.

Ken