I used to be a director of a company that owned a house in a village and was a member of the management committee there. I subsequently sold it and purchased another house in the same village but in my Thai girlfriends name. I was advised that I could no longer be on the committee unless we married and would then in effect be the husband of a house owner.

Does anyone know if this is Thai law or just the rules from our village.

If it is similar to a condo you would not be allowed, you are not a Co-owner and have no official recognized relationship with your girlfriend. I believe if you were officially married with the appropriate documentation you, as the spouse of the owner would be permitted to sit on the Committee. (If the same as a condo)