If anyone is interested, I have since been told by a German lawyer that my hunch is correct. A tenant cannot be kicked out until his lease expires. His presence will also be noted in the buy-sell contract, though he does not have any de facto rights.
On the subject, can anyone recommend a good property lawyer in BERLIN ?? Someone to look through the contract for me?
Although I try to keep my advice on Germany as personal and impartial as I possibly can, I am a businessman with German interests in real estate and it may be construed as a "Conflict of interest" or just me "Touting for business". I am an agent and am not above this under certain circumstances. Dealing with a potential legal advisor is an absolute no-no for me and my business. With this in mind I cannot and will not give you my company details or advise you to use our legal team.
The best (and most ethical) advice I can give you is to contact the British Embassy in Berlin, they will have a list of English speaking legal advisors and you can make your own choice. Good luck with your investments in Germany.
BTW - Are you really sure you want to get rid of your renters? If they have been there for some time and have been problem free and regular payers then surely they can be seen as an asset and not a hindrance to further riches. I personally love sitting tenants as it means I don't have to bother with advertizing the property. Within the limitations of the miet speigel you can raise the rents if y ou feel it is prudent to do so. With negotiations the miet speigel can even sometimes and in some areas be talked around.
A tip - Don't try to be too greedy, a certain 5% income from a long and loyal renter is better than p-----g them off and them moving out leaving you with no income and a hundred potential renters who probably won't be willing to go above the 5% mark as they probably know the local market better than you.
Treat your renter well and they will probably stay with you a long time - p---- them off and they can give you a hell of a headache if they are of a mind to.