Speaking as a fossil, coming from the era when there were "canoes" "kayaks" and "boards", a sit-on kayak is a "sityak", it ain't a kayak. My friend Quinn, the Mighty Eskimo, will be glad to let the walrus explain that to anyone who can't figure it out.
Kayaks are DESIGNED TO BE TIPPY AND EASY TO ROLL OVER. This is so they can be very maneuverable, which requires leaning (heeling) into a turn. And, they are also conveniently tippy so you can do an "eskimo roll" and quickly and easily get an inverted one rightside up!
So, towing it without anyone in it? I'd expect it to do what is natural and INVERT itself pretty quickly. Of course, if you have the spray skirt in it, no big deal, it will probably roll back up before a lot of water gets in. Maybe.
But if you had two, you'd be better off bolting on some deck hardware, lashing them up as a simple catamaran, and then letting them be stable in that configuration.
Otherwise...I think we've all seen how that movie ends.(G)