basically wait for them to go
I would be there, unless you have an agent
as you need agreed stuff like
arrears of council tax, last elec and gas bill and utlities which they are responsible for until the day before they leave and you are responsible for from the day they leave.
the problem-ish is if they decide not to leave on the day.
There is no lgal mechanism to get an eviction-order-just-in-case
on the day they leave
get them to sign a surrender of lease letter
and sidn for handing over the keys ( you clearly sign that bit)
it is not their going which is the potential prob
iut is if they DONT go ....