1. The settlement agreement, if approved in a form of an Order by the court would be enough to confirm/validate the Partition Deed.
2. No, the process cannot be executed in absence of Daughter4. You will have to make her a party in the case. The court will send her summons. If she refuses to come, the Court in that eventuality may proceed exparte.
3. With regard to preventing daughter 4 from challenging her share, you have to stress on the settlement agreement which was duly signed by her. The same can be done during the registration of the settlement as approved by the court.