Easiest solution would be surge brakes on the pup trailer (second trailer) similar to what is used on the tongue of a lot of boat trailers. With that said, I personally would never double pull anything remotely heavy enough to require brakes on the pup trailer. I know it is done, but I'm not gonna be "that guy". My two cents...
Lee, Edith & Lil' Bit the furry feline alarm clock
22 MHC 331RL, Surge Guard 35550, SumoSprings, disc brakes, 412Ah Lithium, Gen 3 Goosebox
22 Ram 3500 CC DRW 6.7 CTD