My 8 year old seems to live on FIFA at the moment, albeit on an Xbox One, so my thoughts may not be completely applicable:
1) do they all offer reasonable offline gameplay (i.e. without XBOX Live sub)?
Yes. My lad only plays offline, as I’ve decided he’s too young for any online gaming. Plays full matches against the computer and the computer seems to adjust the skill level as he’s getting better so whilst he doesn’t always win, he does enough to keep him interested.
2) Is the latest version a must or will a 7yr old be happy with 12, 13 or 14 etc?
My lad has been playing ’15 for a while, and we’ve just got ’17 as a ‘prize’ for a good school report last week. The graphics are slicker, and it was this season’s teams and strips. But not much in it unless you’re a rabid footie fan.
3) Are they all able to be played multiplayer (2up) offline?
Not tried that.
Best way of buying it I found was with an ‘EA Access’ pass. A year pass from Amazon is 19.99. This gives him access to about 45 EA games, all the FIFAs included. Bunch of other good stuff as well, not all of which he can play mind. Games need to be downloaded, and access is only for the year. But frankly, he’ll be bored of them way before that anyway so it was 20 quid well spent.