Serving Notice on tenants

I am currently letting a 3 bed house to individual tenants (2 single men and a DSS couple) therefore three separate tenancies.

Unfortunately I am less than 2 months into the tenancy and there have been persisent and growing problems with the DSS tenants who use the washing machine excessively and do no cleaning at all thereby leaving the house in a disgusting state.

Whilst the other 2 tenants have behaved impeccably, I feel the most practical course of action would simply be to serve notice on all four of them rather than singling out the DSS couple as their behaviour could worsen.

What would I be required to do (e.g. serve a Section 21 Notice or what about accelerated possession ?. Essentially I want to let them know that I will not be renewing their tenancy at the end of the six months and they are welcome to find alternative accommodation any time prior to this date without giving me notice. Also anything I should be aware of when serving notice on DSS tenants?