The Fallen Queen (Titans Book 3)

The concluding book of the Titans series ramps up the stakes. The bad guys are set to not only take over earth but all planets in the universe. Their "home" planet is actually a planet that was occupied by another group before. There are various skirmishes and a unified plan by Titans, Greeks and others. However, odds were not looking good. Then the book suddenly came to a conclusion. The queen was killed, then all of the others started to fight for dominance. The "friendly" daughter ended up becoming queen and suddenly all the mimics stopped and world peace was in place. 

The Missing (Titans Book 2)

The middle Titans book continues with escalating stakes. The mimics have infiltrated earth and are set on planetary domination. There are many cases of travel through the solar stream. It is hard to tell who is a good guy and a bad guy. The remaining real titans teamup with the snakes to try to defeat these mimics. Flying horses gett sot from the sky. This book is really not a standalone book and builds off the first and leaves many holes unresolved for the next.

Titans

Titans is a sequel to the Pegasus series. The Titans and Olympians are at peace. the kids are all going to school. The book is much more lighthearted than the Pegasus books. It also as written intentionally as a multipart series. This book ends on a cliffhanger with nothing wrapped up. 

Random beings, including humans start showing up on the Titan planet. The adults try to lock them up, but the kids realize something is going on. It turns out there are some shapeshifting monsters on the planet that are masquerading as beings that they captured. A ragtag group of kids sneaks into preison to find real Titans and Olympians and escape to earth to prepare for a battle royale.