The original proposal referred to in this question is the proposal submitted by East Sussex County Council, Eastbourne Borough Council, Hastings Borough Council, Lewes District Council and Rother District Council for 2 unitary councils in East Sussex and Brighton.
You can find the proposal here: The Proposal – East Sussex Councils
The criteria referred to in this question were set out in the invitation letter sent to councils in East Sussex and Brighton and Hove on 5 Febraury 2025.
You can see this letter here: Letter: East Sussex and Brighton - GOV.UK