Sellers want to be moved by Christmas - not going to happen is it?

[redpickle]

After three months under offer, we finally found somewhere and had an offer accepted a week ago. We're in a chain of three (our buyer, us and our vendor) and all starting the conveyancing process now. The sellers solicitor has indicated that they want to complete by Christmas. We'd really rather not rush to move in as the house needs work, we have young kids and we'd rather have Christmas here and move in the new year.
I'm thinking that as it's so unlikely anyway, it's probably easiest just to say "yeah, yeah ok" rather than refusing and causing unnecessary issues. We need a full survey, our buyer will be having a home-buyers and from what I understand, there is a bit of a delay on this anyway.
Please tell me I'm right and it's not worth worrying about as they're being unrealistic? They're moving into a new build, so it probably seems quite straightforward to them. I've seen the buyers/sellers rollcall thread so maybe I'm a bit more cynical

When we bought this house, we sold our house at the end of August. we’d initially bought another(new build) house before this one, with a moving/completion date of 30th October. Everything was in place.
But after visiting less than a week beforehand, it was clear that the house we were buying was not going to be ready. Despite the bullshit the house builders were giving us. Saying it’d be done by our moving date. (Build wasn’t actually finished until the following March!)

So we pulled out and had to find another house quickly and start the whole buying process again. This house was in the final stages of the build and we were initially given 15th December, but they finished earlier so it was ready to go on the 8th. Our buyers wouldn’t agree to earlier date, so we had to wait another week for them.

So if you’ve already been under offer for 3 months then more than possible to be in by Christmas.

But what you can’t do is agree to this then decided to stay put. You either agree and be prepared to move before Christmas, of course it may not be done in time but you need to be ready just in case.

Or just be honest a say you are not prepared to go before Christmas.

I can understand your sellers want to be in their new house ASAP. And I should imagine your buyers will not want to rent any longer than necessary, so may want things to move quickly.