Okay great. So VS > VS > FH is a viable option.
No.
Vsx2 is light+light= end of skillchain.
the best way is fh+vs+vs for double light.
Fh+vs is light by fragmentation+fusion, so the skillchain is still open. The second vs generate light by light+light, and the skillchain is closed.
Another choice is vs+fh+vs, vs+fh+fh and fh+vs+fh but you should favor the highest dmg ws in the end of skillchain to generate the max dmg combo.