I am sorry but that is unlikely to work and you are under a fundamental misunderstanding over your ownership.
Originally Posted by Helen80
This will work.
You own the flat under a lease and a share in the company that owns the freehold, while related they are two entirely different ownerships. If you cease to be an owner no matter what you do with flat 3 you aren't entitled to the rewards.
What you can do is
1: extend your lease if necessary and
2: then grant an under lease of the flat ( I suggest 999 years at a peppercorn for you, and 125 years at ground rent comparable locally to be sold) and
3: where the under lessee covenants directly with the company to pay the service charge direct.
You need not invite them, nor are they entitled to a share in the freehold company.
That way you can reap the sale of lease extension on flat 3 and in due course sell the head lease on your flat to the underlessee or AN other.
Based on the information posted, I offer my thoughts.Any action you then take is your liability. While commending individual effort, there is no substitute for a thorough review of documents and facts by paid for professional advisers.