What happened to Aisha and Billy?

At the end of Mighty Morphing Power Rangers Tommy, Kat, Rocky, Adam, Billy and Aisha were turned to kids by Ritas father so the only way to return back to their old lives was to find the Zeo Crystals and use its power. Only Billy was able to find his Crystal by the end of the MMPR season so he returned back to his normal adult state. When Aisha found her crystal in Africa she met a local girl named Tanya (they were about the same age 10 or 12) and Tanya saved Aisha from a lion so when she took Aisha back to her village Tanyas Grandmother or Godmother I cant remember revealed she had the Zeo crystal and gave it to her and also told Aisha she was native to Africa. So when it was time for Aisha to return to the power chamber she told Zordon and the rest of the team she was going to stay in Africa and Tanya would take her place and bring the Zeo crystal with her because Tanya told her that all the animals were dying and getting really sick. Aisha mentioned she took care of animals back where she lived so she decided to stay and help the sick animals. Zordon told Aisha he had a feeling that one of them would not return so what Zordon said he would do was he would teleport her parents to Africa to be with her and would erase her parents memory of having any memory in the States so they would think they were natives in Africa the whole time. The actress who played Aisha (Karan Ashley) said that her decision to leave the series was because of the demanding hours. She also reveals that she was to be given an exiting story arc like Amy Jo Johnson (who played Kimberly). Instead, following time off while her character was reduced to a child for some time in the third season, she would find that she was not asked to return to the set, as her character's recovery would not require her to appear on screen.

As for Billy the way he returned to normal was by using a device called the Regenerator which turned him back to normal when he was still a kid but it had a side effect. During the middle of the Zeo season Billy found out he the Regenerator had a side effect which was aging him quickly to make him gain 20-30 years every couple of hours. The only way for Billy to return young again was to go the home world of the Alien Rangers called Aquitar (they replaced the Power Rangers when they were turned kids for a short time. The mini series was called Mighty Morphin Alien Rangers)and they helepd them in their time of need. Billy had to return to Aquitar with Cestria (supposibly the Pink Alien Ranger but she never morphed or fought) he first met her on Aquitar when he went to Aquitar the 1st time with the Blue Aquitan Ranger Cestro (believed to be Cestria's Brother). The reason he had to go to Aquitar was so he could drink water frome the Eternal Falls (a fountain of youth in the Aquitar Ranger world though never tested on humans) the water worked and Billy became young again but decided to stay on Aquitar with Cestria because he fell in love with her and that was the last time he was on the show. What was messed up was when Billy became young again he talked to the team use the viewing globe to tell them he was going to stay in Aquitar and it was Billy talking but it wasnt his voice! they used someone else! Now the actor who played Billy David Yost left the show because of contract issues with Saban Entertainment and had barely and scenes in the Zeo season so he left on bad terms which is another reason David Yost probably wouldnt even want to come back to Power Rangers Turbo movie because his characters role and his decision to leave the company on bad terms.

Sorry it had to be this long to explain what happened lol

At the end of MMPR season 3 before Zeo, Rocky, Aisha, Kat, Tommy & Adam (as kids) were sent back into time by Zordon to retrive the Zeo crystals, Aisha decided to stay back in the time period she was in, so she gave the Zeo crystal to Tanya and Tanya came back to the present in Aisha's place. And for Billy, during Zeo, Billy decided to go and stay with the Alienrangers to keep them safe I think. I can't really remember because it's been ages since I last watched Zeo