Its the problem with the "chain" situation. If one person falls out, the whole thing collapses.
House buying / selling is not at all conducive to the way most people live their lives. The easiest transaction is an empty house in an executor's sale where you're selling to a cash purchaser.
The hardest is when a family is selling their family home to another family who are also selling their family home and the first family are buying a family home from someone who themselves are buying another family home. Everyone has a mortgage and wants to sell and buy ( and move in) on the same day so that they don't have to rent/camp out with family. But each person in the chain needs to know the funds are going to come through in each link.
And if everyone has a loan approval clause, then no-one has any degree of certainty until almost the day they are to move out/move in.
The answer? Sell first, store furniture, move home to mother and be ready to buy in a few months time. The concern? Prices may go up. Loan approval may be withdrawn
And on. And on.
There is no quick fix solution.
mf