so regular room with extra beds? nope, as far as the FS website says, rooms are not an option with 3 kids. you would have to get 2 rooms.

if you get the upgrade at the skyloft, that seems like the best bet. but it sounds like $1200 is too high, and you might not want to risk it, even though most of the skylofts are 2BR units. maybe you could try making the reservation, and asking the hotel to confirm the upgrade since its your husbands 50th.. the other thing about getting skyloft is the concierge. you have VIP access/reservations/seating at any show/restaurant/etc at the MGM Mirage properties, including Bellagio etc.

if not the skylofts, id think connecting rooms at the FS or Bellagio would be the good FHR options for such an occasion.

although the Venetian does also have a concierge level in their venezia tower, and they have a room type that has 3 beds.. concierge bella is the name, from $500

-skylofts 1BR with confirmed upgrade, from ~$600 (FHR including taxes and transfers)

-venetian venezia tower concierge bella, from ~$550 (FHR/best including tax)
-connecting base rooms at FS(from ~$600 best rate including tax for 2 rooms)
-connecting base rooms at Bellagio(from ~$400 FHR including tax for 2 rooms)