Same Sex Marriage?

Yes, yes they can.

Of course they can. When seeing your signature photo I first thought the mother plant was going to marry someone, LOL :)

Yes. No mods needed.

If you are using MC Command Center, there is a setting for how many many same sex couples are allowed and it is recommended from my experience to sex this percent to smaller because otherwise the game will have pretty much ALL same sex couples. That is NOT a bad thing, but it needs diversity.