Does everyone have to exchange on the same day?

[MaryPoppinsPenguins]

We're at the bottom of our chain, in rented. Our vendor is buying a house from a guy, and he's buying a flat that's empty...

DH & I want six weeks between exchange and completion, which our vendor is happy to do... Does she have to exchange with her vendor, and he with his, all on the same day? Or can we do ours with her now, and she (and he) a few weeks later?

Just so long as we all complete on the same day?

It's unlikely, though not impossible, that your seller will want to take that risk. She could commit to selling to you and then have her purchase fall through and be rendered homeless on your completion date.

Agree with mysteryfairy. Highly unlikely because if your vendor exchanges with you but not on her onward purchase, she leaves herself very vulnerable. Her onward purchase could fall through any time before exchange and yet she has committed to selling her property to you. Too risky and her solicitor is unlikely to agree to this. This is precisely why it sometimes takes "forever" to get to exchange, because everyone in the chain needs to be ready first!