My only "must" is that the 4 new teams should each get to play OU and UT at home one time before the departure. Assuming they're still going to be around for 2 more years ('23 and '24), there's plenty of space to make it work.
At this point, if I were the Big 12 office, I'd already have the matchups done and now be scrutinizing other P5 conferences' schedules to find where their potentially ****** weeks are -- then slot the "best" Big 12 games on those weekends to all but guarantee the best network spots.
So assuming if the Big12 is creating a 2 year home & home schedule, your saying OU/UT's schedule the next 2 years would include 5 current Big 12 teams and the 4 new teams each year? How does that make sense, unless you want to ensure that OU or UT are Big12 champs.