If you can manage it, it is possible to keep people like that at arm's length but always make sure you can NEVER be accused of saying somerthing to them.
For example, my creepy stalker (who has been behaving himself for years now). Although I have spent years cutting him dead in public, I am comfortable with saying hello when we pass as long as there are independent witnesses that I have not divulged any information nor said anything which can be quoted against me. At one point I said, "Hello" to him as I was walking past, and I later heard he was telling people I swore at him. As there had been witnesses I immediately went to my witness and asked him to verify that I had not said anything other than "hello."
There have been many times I wanted to confide in someone. Other things such ascollecting medications from the pharmacy - the pharmacist is clued up to not let ANYONE see what prescriptions I collect, even the most innocent-looking. I bring a large flour bag and our medications get put into that, and the pharmacy staff know to not mention the name of anything. I've already had my stalker announce to half of Sydney that I'm an addict, that I'm unstable, that I have Munchhauesne's by proxy, that...
So I even stopped confiding in my closest friends, although over time I have learnt who I can trust to keep mouths shut, and who to not risk confiding in.
It has been tough at times, wanting to unburden to a good friend but not being able to say anything.
The important thing to always remember - nobody values your secrets and the need for secrecy, more than you do yourself. Never confide in someone what you want kept secret, unless you're prepared for it to slip out. Especially if you have a'stalker' who is a skilled interrogator. A friend minding a confidence is less motivated to keep mouths shut, than you yourself. The best way to ensure that friends won't accidentally leak to someone masquerading as a good friend concerned for you, is for your friends to simply not know anything.
Example - I've told people this one before. I was asked by a friend how my job was going, I mentioned how we'd put the latest journal issue to bed (it had gone to the printer, the rush was over) and how I was enjoying a few weeks' lull before the next rush.
SHe next went to the coffee shop and I can picture the scene - person masquerading as 'friend' of mine asks how I'm going, she says something like, "she's enjoying a few quieter weeks at work now the latest issue is finished."
Next thing I hear, everyone is being told by 'friend' (aka stalker), "Poor Marg, she's had her hours cut back and is about to lose her job."
I had made an innocent remark to a genunine friend, I hadn't even said, "Keep it to yourself" because I really didn't think there was anything in what I said that could be twisted - and the creep found the chink, stuck in a knife and twisted it.
So I learned to REALLY pull my head in about confiding in people, even good friends. When someone I met said, "Hi, How are you?" I learned to reply with, "Hi! Great to see you!" in reply, certainly not answering how I was. THAT info has been locked away for a long time now. And it's amazing how few people ever notice that you didn't answer how you were.
So now your sister is in the same category. And your father. But it shouldn't be too difficult for you - all you have to do is remember to get them talking about themselves, they will never realise you've not told them anything about yourself or your opinions. What is more, they will consider you to be a witty and sparkling conversationalist, without ever realising or thinking about you not having said a word other than, "Tell me how things have been for you."
it's amazing how witty people think you are, when you say, "uh-huh" at all the right points.
Marg