So how many routes are there in this game and how/where do the diverging options for the routes begin?
There are: a route per man, one Owain, one Emrys, one Mordred that all amount to the same thing, Gwen going with them rather than Carwyn. For each of those routes you can also run fem Carwyn and/or corrupt Viv or Carywn with Viv.
So that's Gwen cheats + Carwyn and Viv options
There is also the slut Gwen route that involves her cheating but also classing into erotic dancer rather than warrior. to do this have her get lots of gropes with the boys and then class her into dancer asap, not sure on the level number you need but it's not before map 10 that's for sure. This has all the guys sharing Gwen in the late game except Carwyn. This also has Viv and Carwyn options like above but those have different ending options though the routes are the same.
There is also a Carwyn and Gwen route and a Carwyn triumphant or Carwyn + Gwen + Viv route.
In summary there is:
A cheat route for Gwen and each guy: simply have them grope her most and your good.
A slut Gwen route: have her on a cheat route and class into erotic dancer and not warrior and keep the gropes coming.
A fem Carwyn route: have him transform and get groped enough.
A corrupt Viv route: have her stand near ally robots/deploy the robots near her and her chip will react.
A Viv + Carwyn route: don't have robots trigger, don't have Carwyn on the slut route, do have Viv grope Carwyn a lot and don't be on the pure Gwen route?.
A pure Gwen + Carwyn route: no gropes for anyone, i don't think it matters what Viv is doing so long as she isn't groping Carwyn.
A threesome Carwyn + Gwen + Viv route: I think you need to be on the Gwen + Carwyn route and have Viv start groping Carwyn, though i can't say i've done this route yet.
Routes don't diverge early, there is also a supporting word doc in the download that gives a very good set of instructions and exact timings for routes, which begs the question; why did i just type this out.