Donnie, I can't attest to how dragging two sleds at one time works... Worst case is that you braid yourselves together I suppose. A buddy is supposed to be within touching distance anyway. I see the birth of a new California trend...
Full Contact Sledding! Alternatively, you could simply build a "double-wide"... one tow point, a big slab of wood and "Bob's yer uncle"! I have no idea how you'ld steer it though...
To be serious for a moment, you do need to be careful with this stuff. In these parts, the biggest risk (apart from the usual diving stuff...) comes from fish nets. Around here, there is still some commercial fishing using monofilament nets. Many years ago, we "found" a lost one when we towed a friend right into it. He released the board (via the spiffy quick-disconnect!) which wasn't uncommon, but neither he nor the board surfaced anytime soon. After a period of time, I started to suit up to go see what he had found, when he popped up after spending "some time" cutting himself free. This guy was a very capable diver and I think in hindsight that a "lesser" one might have become one with the salmon! Make certain that you have at least two cutting tools. I generally always carry a knife, shears, and a "zip" knife...
Incidently, all of that hardware (track, sliders, quick-release) is standard sailing stuff, available from your local chandler!