How do I use RTG but also keep the mods like abyssalcraft and what not? When I have the mod JustEnoughIds It says RTG is the problem and when I remove JEI it says abbysalcraft is the problem which I assumed is biome ID.

JEIDs is the problem, Minecraft doesn't support more that 256 biomes in 1.12.2 and RTG expects this behaviour as well