For all fights bring blood vials, more is better.
Smaller ones like Stego can be killed with with a leveled Dodo Rex, maybe other bosses might work, but Dodo Rex is the strongest.
The stronger ones like Primal Tek Quetz need a (leveled) Primordial, best way is Nephalem, the primordial Dragon, he can also dive to fight the primal tek Mosa.
Killing he strongest one - the primal tek Giga is hard even with Nephalem, you can try with Beast of Darkness or one of the two Supremes, but that's all endgame content, an i have no idea if everything works well. The mod is outdated and has some bugs. I stopped playing it after the kibble rework and have no more hope, Psycho comes back to uptadte.

Thanks LoneWolf !