As the Rule states, you may only purchase one Private estate and be the Master (owner) of one Free Company with an estate attached.

1. Is fine, you can own a personal estate and be the Master of an FC that has a house attached.
2. 3. 4. and 4b are against the Rules, you could only be a member of another FC on the same world with another character, not be Master of two or more FC's with alt characters on the same account.
So as you pointed out it is technically possible to be Master of up to eight FC's on a single account.

Do or will they act on this Rule, I don't know of any reports so far of any action taken, but they can and maybe will.
Best to not place yourself in the Rule breaking category or later on you may loose the FC/House/Account. You could try reporting FC's you think are breaking the rules.