Ending Tenancy Early

Rent Arrears

Hi,
My tenants want to end the tenancy early as they have separated.
They are also struggling to afford the rent. They have a guarantor, however they are 5 weeks late on rent (they have missed 2 payments) and the guarantor says they can't pay as their circumstances have changed since signing.

I am happy to end the tenancy early. They have both confirmed in writing that they want to. It is 6 months into a 24 month AST.

I have read the NRLA advice about using a deed of surrender.

My question is about the timings of ending the tenancy now and finding new tenants.

Can I end the tenancy immediately, but still ask the current tenants to pay rent until new tenants move in?
If not, can I agree to end their tenancy only when I have a new tenant starting their contract?

I'm concerned that if I end their tenancy now and it takes me several months to find a new tenant I could have several void months.

Many thanks
Sam