You are on the ball as ever
Estelyn! 
Well,
Mithalwen, if you are right about this so called 'twin brother' then I guess we should track back to all the mentions of Ferny in the book and look for bits which just don't feel right....
Once when drunk, Aragorn proclaimed that Bill actually had a twin sister as well. He claimed that she had 'come on to him' big-time in Bree. Merry and Sam in attendance were not sure what to make of this claim.