For the Big 12, the ratio of FOX (Fox, FS1, FSN) to ESPN (ABC, ESPN, ESPN2, ESPNU) games in any given year is roughly 3:2.
This year, there are a total of 55 games (45 conference, 10 non-conference) under Big 12 control.
What we DO know is that the only CFB on Fox networks this fall should be the Big 12. Their other three leagues (P12, B1G, MW) aren't playing. I'd expect that there will be a minimum of one Big 12 game on FOX and one on FS1 in every week that doesn't interfere with their other programming (e.g., MLB postseason). I don't think there will be enough content left over for FSN.
What we DON'T know yet (but should soon) is the fate of the "school-retained game" broadcast. With fewer games available than in a normal year (missing 2 weeks of non-con), and an overall lack of games nationwide on 9/12, will Fox/ESPN be able/allowed to bump those games up a tier in order to maintain their annual quota of ~33 and ~22 games, respectively? Sub-question: Will the networks want to bite the bullet on the three Big 12 vs FCS games on 9/12 just to fill air time?