I even checked the forum before making the post to see if it was original. Oh well.
Possession and Masq would work the same as printed on the card. I assumed that it is arranged Team A, Team B, Team A, Team B so you are never directly interacting.
The idea of seeing your partner's hand I think isn't really workable IMO. It doesn't work well with possession and would be even worse if it was all the time. Plenty of card games make you make similar decisions without knowledge and I feel that 'table talk' should be forbidden.. but hell, it's your group, your rules. I think it's just the nature of the mutated beast that attack cards would be less interesting. Trying to band-aid the attacks with a special rules is a losing affair that would cause arguments.
As for gardens, vineyards, and fairgrounds I would have to expect they count whatever deck they are a part of.