If you are going to be staying mainly in flat terrain and packing on the lighter side you should be OK. However along with being at the upper limit as to weight you are also at the upper limit and maybe over on the wheelbase side of the equation also.
E rated tires and a very good WD/sway control system may be just the edge you need to get by for a few more years. As for the 1 & 3 year old we went to Florida with ours at that age. We would leave around 7 PM put Barney on the VCR (full size conversion van) and no worries. Drive non stop to Orlando other than gas, food and potty breaks. Pick up a 16 inch portable dvd player to keep the kids entertained and life is good!
Good luck Don