Mike went far in the past. Small changes could cascade, especially with his mental state and knowledge or at least his willingness to work harder than his past self had. For a brief period of time travel Mike had enjoyed getting his manly vigor and passion back, but would happily relinquish it as his balls undropped. He didn't want to have to wade through years 0-3 where he'd be doing very little... Still year 4 he wasn't doing much either, but he'd be enrolled in preschool and could start showing brilliance. Then Time travel stopped and Mike was left in the body of his 4 year old self in his old room which would eventually become Jeff's.
Meanwhile in the present Jeff said "Hey dad! what's taking so long. I thought we were goi-" and then his dad seemingly vanished. Jeff went to the Chronivac which had a window open showing "View of Time Traveler [Mike] 3rd person, 2nd Timeline 1976". Jeff was confused for a bit, but decided that he'd take his change into womanhood and... the Chronivac had locked him out of changing anything in Timeline 1... A.K.A. Jeff's reality.
Katie screamed "Jeff, George, Dad! Mom's frozen in place!" Jeff heard the scream and went downstairs to see Katie was still moving and yet their mother was in completely once place. George came by a few seconds later.
The older brother said "The water seems... Well not frozen exactly, but stationary in mid-air."
Jeff thought for a second and said "Alright guys, let me let you into a secret." and motioned for his siblings to come into his room. They saw the window and Jeff explained that their dad used a reality altering software to travel back in time.
George asked "So... how come we still exist?"
Jeff said "We're in separate timelines... at least right now. I think the way this program is working though is that until he reaches our point in time our reality is frozen, and we can act because... I think the program had some sort of failsafe for certain relatives." He was typing out a few things.
Katie asked "So we're going to be stuck like this for 50 years?"
Jeff said "I can look into maybe speeding up the simulation... Although I'm not finding any good leads so far. I did do one thing for the three of us though."
George said "What, make it so we still get born or something?"
"Well Some incarnation of us at least. So when the Timelines merge while we might now be George, Jeff, and Katie we will still be living as our dad or mom's kids. I'll need to take a look at some other things I can do about our situation, but it seems like I can mess with dad in that timeline and since the chronivac wasn't around... Well he can't do anything to us exactly."
"Why be mean though?" Katie asked
"He was laughing saying stuff like, Yay no more wife or dumb kids. My ticket to an exciting life is so close... Basically the first thing he did with a reality altering software was essentially wipe the three of us out without a second thought. I'm not really feeling that compassionate here. Let's give him one change to at least let him know we're here."
Mike was having a great time at breakfast chowing down on some toast with a slathering of butter, crunchy greasy bacon, and scrambled eggs. No fucking dietary restrictions or special diets. None of that plant based meat or whatever... Real food. Then Mike heard his mom say "Mary, slow down. It's a little unbecoming of a young lady. You even got some grease on your nice new dress."
Mark looked down and indeed he had gotten some grease on a pink frilly dress he was now in. His arm while foreign did look a bit different as well. Somehow he had changed into a girl. How was this possible? he thought and then he realized it was possible the software that had brought him back in time still might be changing his reality... But who was left? Was that time still going? Mary would soon learn soon enough that yes the Chronivac was still going and that maybe one of her kids from the present was changing things about her life.
Meanwhile in the present George asked "Don't you think that may bite us when the timelines merge?"
Jeff threw his hands up and said "Maybe. Then again we've already been bit by our dad deciding to go so far back in the past. Along with who knows how many other people?"
Katie asked "So do we just have to wait now?" already sounding board. They could get some board games and just play. Heck they could all walk to a department store and grab as many of those games as they wanted considering time was just stopped. They thought about what they'd want to do and...