I went in with two Daeodons eight megatheriums a yutyrannus and one megalania to kill the alpha version. I climbed to the ceiling of the cave with the megalania and blasted it with rockets from the roof while the megatherium tanked it and the yuty gave the Megas a buff and the daeodon healed
When you take on the brood. Rush it. If you get your rexs to surround it you can pin it so it doesnt do its poison attack. Rexs will need 30k hp 800 melle and you will need 10. For Alpha i suggest 85+ saddles 40k hp rexs.
19 rexes health all about 25k dmg 550+ min saddle 86 highest 115, 1 yutti with good enough stats,should have worked fine for the alpha but the yutti ran forwards and attacked first before we could mount and died from the start ,recommend keeping the yutti on passive to avoid a disaster like that (alpha difficulty)
5 fuzzy Rexs drains it health with the help of an ar with 250 bullets and it's dead in 25 seconds as long as you pump melee and hp on your fuzzy Rex's ( btw works for all bosses but not the manticore the scorched earth boss if you don't know already).