If 3 are leaking, then you should reseal all of them. You DO remove the windows, clean out all the old stuff and then reseal them with Butyl tape, which fills all irregular gaps and never hardens. Once the windows are back in I'd use Lexel caulk (available at Ace Hardware or online} to seal the outside around the frames. Lexel is a VERY sticky and durable caulk and I (and many others here) think it is better than silicone or other choices for a trailer.
Hi-Lo 1707T - Tire Minder TPMS on Tow Vehicle and Trailer, 300W Solar Battery Charger, Equal-i-zer WDH
2014 F150 Platinum 4x4 3.5L EcoBoost SCrew