How much room do you have on the other side of the tree - or to one side of the tree? My thought is to put the wedding party on the other side so that you are standing between tombstones to take the picture but there's no tombstones in the picture/s. If I understand your description correctly, if you place the wedding party to one side of the tree you may be able to include the church door in the picture.
I'd get some husky relatives to remove the bench as it constrains your options too much.
How about making up a little poster faking a love heart carved in the tree and a real close shot of the pair?