As soon as you start using "omni" you start having problems.
Create something you can't destroy
Or in this case
Create something the other guy can't destroy
Which of them isn't omnipotent, the one who can't create such an item or the one who can't destroy it? Either way, one of them is no longer omnipotent.
The old pantheons had a way round this problem, while they had limits to their powers they also had rules to obey, including:
no god may undo what another god has done - Ovid, MetamorphosesOvid, Metamorphoses
Which meant that if one god had created it, whether the other could destroy it or not was irrelevant, they wouldn't be allowed to try.