^What Jim said... Have it checked out by a fab shop, for the hitch capacity.
Real capacity will be tongue weight most likely. You can't let the 2nd trailer tongue weight cause the primary trailer's tongue weight to become offloaded enough it becomes unstable. In other words, keep the primary trailer at 12% or more.
I have towed snowmobiles behind my TT throughout northern Idaho, and it was still a just as stable as towing the TT only. I will be installing a rear camera before I do this next time. The snowmobile trailer was completely invisible except when going around curves. I puta snow skirt on the rear of the TT (aka mist guard.... looks like long broom bristles) and that reduces snow buildup on the 2nd trailer.