Hello again and thanks for using Just Answer.
To be honest, with all new Builds which are not fully completed, the Contract never stipulates a fixed completion date. Instead, the Contract will stipulate that the completion date will be 14 days after the date on which the Developer's Solicitor has notified the Buyers Solicitor that the property is ready. I would always explain to such a client that the eventual completion date is totally down to the Developer and there is no legla pressure which can be put on the Developer to speed up the completion date. Under new Build Contracts, the only protection a Buyer has is that the Contract has to stipulate "an estimated completion date" and if the property is then not ready for completion 6 MONTHS after the estimated date, then the Buyer has the right to withdraw from the Contract.
I don't of course know the full conversations/written advice provided by the Solicitor, but any Solicitor worth his salt should have explained this to your friend. By the same token, I would have thought that your friends should have known that a fixed completion date was not feasible, as the proeprty is not yet fully built.
Either way, I am afraid the Contract is legally binding, as it has been signed and "exchanged" on behalf of the Buyer. On exchanging Contracts, the 2 Solicitors agree the that their respective copy of the Contract is agreed and in the same terms. On that basis, Contracts are exchanged and becomes a legally binding agreement between the 2 parties.
Therefore, your friends only possible cause of action is against their own Solicitor if they were misled as to the completion date (please note their Solicitor will only have been told of the estimated completion date before Contracts were exchanged, and if he has then subsequently told it is going to be delayed, I'm afraid he can't be held liable for this delay PROVIDED he made it clear to your friends that the completion date was not fixed).
Your friends certainly would not be able to say the Contract is void, and the best they can expect is compensation from their Solicitor, if indeed it turns out that their Solicitor has been negligent in advising them on a completion date.
Your friends are entitled to see a copy of the Contract, although this will just show that the completion date is 14 (possbly 10) days from the date the Developers Solicitor gives notice to the Buyers Solicitor that the property is ready, and the estimated completion date.
I hope you don't feel I have been unreasonable in answering your question.
Please let me know if you require any further clarification.