I never do turkey of any size long/slow in my WSM. I cook poultry at 350*, and I believe most here would also recommend that. Gonna need a lot of charcoal for a 25 pounder at 350, though.
I don't believe a second-- even 10-14 pound-- turkey will fit on the bottom grate with the top grate in place, so you'd have to do 2 of them in shifts.