(Assuming that the OP is in Texas…)
Having a rank below top 25% would make it very difficult to get into UT Austin through the non-automatic admissions, since only a quarter of the spots are available, all out-of-state applicants are competing for those spots, and rank is still important in that part of the admissions (i.e. non-automatic top 8% rank applicants would have an advantage over top 26% rank applicants).
Of course, if the OP’s kids apply to private or out-of-state schools with much less emphasis on rank, or less selective Texas publics, then they could be fine at those schools.