(On the island) There is a pretty easy way to kill titanos (easiest in the outskirts of the redwoods) with just any one giga or carchar (recommended to be 90+ blood rage if youre using carchar)

First things first, you need to aggro it, you can shoot it with a ranged weapon or by hitting it with your dino (most safe to walk behind it and hit its tail) if youre riding a giga, bite the tail first, while it turns around to face you, turn your giga around and wait for the titanos head to be in your face pretty much, from here you just need to walk forwards while biting the head (really easy with the gigas huge aoe) and if it tries to run from you, either chase it while biting its tail or stop and regen stamina, and repeat the previous steps until its dead

If youre riding a carchar, first kill other wild creatures around the area to rack up blood rage and then aggro the titano

Killing it with the carchar is as easy as walking backwards and biting its face until it dies, and when it starts running away like with the giga either chase it and bite the tail or stop for stamina

And thats my preferred method of killing titanosaurs whether it be for xp, hide, or just for fun