We are never told that much about what happened to the hybrids before the show.
I have listed what we do know about the birth and early life of the hybrids below.
The pods 'hatched' sometime in 1989.
Max, Michael & Isabel
Max tells Liz in the epi 'Balance' what he remembers about coming out of the pods.
I remember the first time I saw Michael. It was in the desert the night we first came out of the pods. The sky was bright with stars and this full moon. Isabel and I found each other first. We didn't know how to speak, but we could communicate anyway. We walked for a while, but we could both feel someone else.
He said he saw us, but that he was afraid. So he just watched us for a long time. When he finally revealed himself, he was standing on this rock. Just like you'd expect from Michael. "Here I am. Deal with me." He said it was the hardest thing he's ever had to do...to trust us.
Both Max and Isabel talk about when they came out of the pods at different times, but neither mentions a fourth pod nor Tess.
Later, Tess 'helps' Max remember her being in the pod, and it is a bit different than what he remembered.
Max remembers coming out of the pod and seeing Isabel and Michael already out. He sees Tess still in her pod. Michael moves to the door and opens it to leave. Isabel wants to leave too, and holds out a hand to Max, but he hesitates, looking to Tess in her pod, but eventually takes Isabel's hand and they go, leaving Tess still in her pod.
Perhaps Max just doesn't remember that part later, or perhaps Tess used her powers to make him remember what she wanted.
Whatever really happened in the pod chamber, Max, Michael and Isabel walked through the desert to the road.
Max continues his story.
We all saw the headlights at the same time. Isabel took my hand. We knew we'd be safe as long as we stayed together. I held my hand out for Michael. I knew he wanted to. He just wouldn't take it. So we just looked at each other for a long time. Wouldn't see him again for 3 years. Isabel would cry every night, wondering where he was.
Max & Isabel
Isabel and Max were found by the Evans, and were taken to stay in an orphanage until they were adopted by the Evans.
Michael was left alone and he was found wandering in the desert about a week later and is taken to an orphanage. It must have been a different one than Max and Isabel were taken to, or they were placed with the Evans very quickly, because Michael didn't see them again after the desert for three more years.
Michael was placed with a single man as a foster parent, Hank Whitmore.
Tess tells Max that when she came out of the pod Nasedo was waiting for her. He took and raised her.
Lonnie tells Max that they 'hatched' from the pods underground, where the pods are still hanging. We are not given a date, but it was likely around the same time the New Mexico pods hatched - 1989.
According to Lonnie they also had a shapeshifter protector, but it is unclear of how much the shapeshifter had to do with them, or why or when he/she left.