I found a good emulator for this, Retroarch!

You can play mods with friends just fine using the Remote Play-Together built into steam itself.
Load the romhack, get to the multiplayer selection screen and start the play together with your friend. They won't even need to own the genesis collection.

thank you very much!!

Yes, you can play mods with your friends that have the game too (No remote play need). Both must subscribe the same mod (and have the game that it needs) then you invite him to play, select the base game and press Y to shown the mod.