I had Bilenky Cycles add a kickstand mounting plate to both my Santana tandem and Santana triplet (pictured earlier in this thread). Money very well spent, as it makes the twin-legged kickstand setup rock solid. If you don't have a mounting plate, just be careful how much you torque the mounting bracket and bolt down on the chainstays (as others have noted). Rivindell and likely others sells a "sandwich set" that helps spread the load on the chainstays:
https://www.rivbike.com/products/ple...nt=23336090241