BMlock,
I've done 5 in a family sleeper before, last May on the Auto Train. Actually we had 7, but we had a standard room in addition to the family room. Traded in 50,000 GR points for the two rooms & the transportation of the van.
I put my mom and myself in the standard room, my sister-in-law along with her two sons 4 & 18 months, along with my 2 neices (my sister's kids) 6 & 10 in the family room.
My sister & brother-in-law drove to Florida, while my brother flew down later.
But bottom line we had 5 in the family room no problem. This of course assumes that either you or your wife plans to sleep in the same bed with the 2-year-old. This might not work for you though in another 2 years, but for right now, you're fine. Note, we didn't actually get a ticket for my 18-month-old nephew.