Did the moms already accept your offer for the shower? Maybe take them out to lunch and see if they agree that another shower would be redundant....hopefully they will and you can let the other hostesses know and volunteer to help with their showers.
If they have already accepted and want to proceed, maybe you could make it a small event for just close, mutual friends or host a little spa day (mani, pedi, lunch) instead of a shower. I think many guests would feel put out to be invited to multiple showers unless they were immediate family.
If they haven't given you an answer, maybe just drop it and volunteer to help the other hosts.