Regarding booking an extra seat to ensure that someone does not sit next to me and my wife:
1) Is there much of a risk that we would not be able to sit together, presuming that I book early enough to get three across?
2) Would both the xtraseat and my wife be entitled to free MCE seats, presuming we're on the same PNR? I'm PLT.
3) The better course is to call, rather than book online?
This would be much less expensive than two F seats on some domestic routes, without giving up too much.