Unusual 2 way wiring?

[Bradersmac]

Can any one help me figure out what’s going on here? Down stairs light switch is 2 gang, 1 gang is one way controlling downstairs hall way, second gang is 2 way controlling top floor hall way. Upstairs switch is 1 gang two way again controlling upstairs hall way light. So wiring seems weird. Downstairs , gang 1 has live into com and switched live into l1, great. Gang two has a bridge into the com, and pos and neg into l1 and l2 . Upstairs 1 gang 2 way has 2 x 2 core ? Pos and neg from one into com, and pos and neg from second 2 core into l1 and l2. Guessing one of the 2 core being used as strappers and one being fed from light? Any insight?

 

[jj4091]

Yes your thinking is correct explained here by diag. https://www.diynot.com/wiki/Electrics:Two-way-lighting