Congrats thats awesome, my family is pretty notorious for twins both my mom and dads side I lucked out and never had twins.
But I did/do haul around my two + someone else, I have been watching a friends two sons one is four months and my kids two car seats, and the new born seat, fits fine in our 2015 Subaru Outback where it would not have in our 2007 Grand Cherokee. So if it is just dirt roads it is a great option, it actually is a little better off road than the GC was, I just miss the Hemi, also the OB gets great MPG's, in city around 25.
Depending on your year of 4runner though, they seemed to have about equal space when we were looking, the Tundras had tons more space, and Cummins had even more space (one day) but for us not the option (price, MPG) we needed.
Also not sure on the option but my dads Yukon has second row captains chairs, so when we get together he usually hauls 5 of the grandkids just fine, it is easy in and out and real comfortable to go hunting in as we are all
6'+ and 200+lbs.