Basic Plot Outline of my series Monster Adventures how many books should it be?

basic plot outline of my book: Korrow and his children live on an island on the Bermunda Triangle to avoid humans due to their powers / witchcraft they accidentally release Satan and they beat him, which leds Korrow to leave the island with his kids, there he finds his older kids who were lost at sea years ago, and his uncle with his ship which he stole years prior after returning back to the island, leftover demon lords from Satan's release teams up with an alien to take over the island and a human crashes onto the island, his Uncle is ressurected once more and battles Blackbeard and his Uncle's fountain of youth water is shipped out to Flordia causing mutations, causing Korrow and his kids to go to the mainland to deal with it leading to Korrow's death, the kids must team up with Pangea and Korrow's mother to save Korrow, Korrow and his crew then go to the gods to get an answer why their people are negelted, while fighting an undead king. Korrow would then spent two books fighting Lucy an old ally, then a dimensional rift would open up having variants arrive leading to the Shadow Lord finding a way over, the US Government would raid the island and they would have to fight them off, Korrow then spends 2 more books defeating the Shadow Lord should this be 7 books or more?