If you are planning to do a bank transfer when they leave I am taking it that you did not put their deposit into a protection scheme?
If not you better read this www.gov.uk/tenancy-deposit-protection/if-your-landlord-doesnt-protect-your-deposit
They do not have to allow viewings at all unless they are within the last 28 days of their tenancy.
You cannot just chuck them out if they stop paying, it has to go through court and any threats or action prior to this could land you in massive trouble legally.
Secondly if they do require social housing then the council will tell them not to move and to stay put until the baliffs from the courts turn up because otherwise they will be considered intentionally homeless.
If they stop paying because they cannot afford rather than wilfully they will not be intentionally homeless.
You have to serve the correct notice whether that be section 8 if you are within the fixed term tenancy or section 21 if not.
You cannot
Enter the property without permission
Forcibly remove them or any of their property
Change the locks
Sign up new tenants until the old ones have left
So they won't be out pretty sharpish and they know it if they stop to pay at all.
In regards to their guarantor the guarantor is for the rent payments if the tenant stops to pay. I am not 100% but I am pretty sure that the guarantor is not responsible for any court fees unless you actually take the guarantor to court for non payment themselves.
I have never heard of a guarantor having to pay for damage to the property or cleaning or such but possibly they do?
In fact I have even heard cases where if the guarantor deed is not signed and independently witnessed it being rejected.