SEC is already at 14 teams with no danger of losing anybody. B1G currently has 14 teams as well. ACC is at 14 teams plus their affiliation with ND. B12 would need to add 4 teams. In this scenario I think they add UCF, Cincinnati, Connecticut, and Notre Dame. The P12 then adds BYU and Boise State. Here's what those 2 conferences would then look like:

B12
North:
Cincinnati
Connecticut
Iowa State
Kansas
Kansas State
Notre Dame
West Virginia

South:
Baylor
Oklahoma
Oklahoma State
TCU
Texas
Texas Tech
UCF


P12:
North:
Boise State
California
Oregon
Oregon State
Stanford
Washington
Washington State

South:
Arizona
Arizona State
BYU
Colorado
UCLA
USC
Utah