How to go About Reporting a Cheating Guild?

Here's my advice: don't report this guild. You would be wasting everyone's time. 

The reason those teams have the same GP, is that a character's GP is calculated by a formula. If I have CLS at r5 with 3 zetas and 6x6E mods, his GP would be exactly the same as someone else with the same investment. The teams you showed in the screenshot all have exactly the same relic level and zeta count for each character, and when I checked the guild on swgoh.gg it was clear that all those squads had 6x6E mods on them. 

Also, when I checked on swgoh.gg, none of the players had exactly the same GP, and I'm not sure what you're implying is going on with similar last activity times. How could that possibly be suspicious? 

But, most importantly, when I checked their TW record on swgoh.gg this guild has a 10-167 W-L record. The last time they won a TW was 31 May 2022. Even if the things you find suspicious were the result of cheating (which they aren't), why would any guild bother to cheat at a game they are clearly incredibly casual about?