Subpoena of a witness

If plantiff and defendent want to subpoena the same person to testify in court do we both submit a subpoena?
I am aware that my ex already sent a subpoena to someone I want to use but wondering if I should also send one b/c couldn’t they dismiss them having to come for their subpoena. I want to make sure they come for my questioning.

Yes, the person issuing the subpoena has the right to release someone from their subpoena, so if you feel this may happen, it would be best to also issue them a subpoena.

What is the difference of issuing a subpoena of a witness versus an getting an affidavit?

A court doesn’t have to accept an affidavit into evidence.