There is a BOOK series call Roswell High. That is where the idea for the show came from. I have to say the book series is much better. At the end, Alex is still alive and Project Clean Slate, known as the Special Unit in the TV series, is completely destroyed. However, there are some secondary characters that die. Adam, the sweetest alien ever, is killed by the cruelest alien ever, known by his Earth name, Dupris. Sheriff Valenti is majorly evil in the book series, and is killed by Dupris. Nicholas, another alien, is killed by yet another alien named Ray. Ray is different from the others. Max, Adam, Nicholas, and the others were in their pods when the ship crashed. Ray was the only already-born survivor. Ray is a good guy.

There's this cave in the middle of the desert, it's more like a hole in desert floor. You'd never notice it if you weren't looking. That's where Ray took the pods as Dupris, the evil alien was killing everyone else, and the humans were showing up to do who knows what. One pod held Max and Isabel. They were twins. One held Michael. Another held Nicholas. The pod that held Adam was not resued, and was found by Project Clean Slate, which used Adam as a tool to find the other aliens. Nicholas broke out of his pod before the others, carried it off with him, was adopted, and moved to California, only to show up in the second book of the series, The Wild One, I believe.

Anyway, the important thing is that Max and Isabel shared a pod. That is how their DNA got mixed in together, creating another life.

And let me clarify that there was no PREVIOUS LIFE. They were simply unborn when they were in the pods. That's how their lifecycles go, like humans being in the womb, or birds being in eggs.

There is one book where Michael is captured and Isabel feels a connection to him, which makes her think they were meant to be together. But that idea is abandoned in the last book, when the couples are Michael and Maria, Isabel and Alex, and Max and Liz.

And guess what! Michael has a brother!

Anyway, enough of that.