How can I give permission for tenant to have lodgers? Use Class C4?

[bureaucrazy]

How can I give permission for my tenant to have lodgers and keep it all documented correctly?

I wish to grant a tenancy to one reliable tenant who I trust who will pay the rent and the bills at my house. He wants to have his friends as lodgers and he will charge them all inclusive rent for each room. Tenant will take responsibility for the lodgers and is liable for the full rent to me. Usually I would opt for a joint tenancy agreement. However, the lodgers cannot necessarily commit to the full 6 month tenancy and may be replaced by new lodgers. Admin wise it is much easier to have a single point of contact, plus T will give me a 35% higher rent with this arrangement. If I try to have a joint tenancy, people will move in and out behind my back anyway and I will have trouble collecting rent from incoming residents. Some of them speak little English and do not follow rules very well but on the whole they are OK and just need somewhere cheap to live. Is there anything I should stipulate in the AST?

Can I do the following?

"I could stipulate on the tenancy agreement somewhere that I give permission for the Tenant to have up to 3 lodgers who are not related (but no less than 2) on license of the Tenant who he is responsible for and that he must record their names and DOB and dates they move in or out. I will also stipulate that they must share the property together as a single household would."

My main concern is not to lose my C4 (HMO) use class more than anything else. The council have an article 4 direction but my street is not listed. Do I need to do anything to protect my C4 use or can it fluctuate between C3 and C4 with out any trouble? (e.g if only 2 people reside for a few weeks).

Even if you can't give sure advice i'd appreciate opinions