Yes, yes, it does show the value system in which your dad - and whole family - have lived. I repeat, you are a marvellous exception and I hope you will encourage your promisingly exceptional niece!
What I am going to suggest is what you've suggested endlessly to yourself. Perhaps it will help to have it said by others, in other ways. Adopt the principle of I'm OK, you're OK. (Here's the book, if you don't know it.) It is a fundamental assertive principle that you are the only qualified judge of your own behaviour, and everyone else is the judge of theirs. This doesn't stop you having opinions. But it does presuppose everyone's sovereign right to be treated with respect.
When your sister chuckles patronisingly at your modern ways, one assertive response would be with DESC scripting (h2g2.com/approved_entry/A2998551 three-quarters of the way down]].) In this case, your assertion would be something like: "When you belittle me like that, I feel you look down on me. I'd like you to acknowledge my point of view, then we'll get along better."
A related approach comes through Transactional Analysis. You sister has gone into Parent mode around you, and you've unconsciously reacted by feeling like a frustrated Child. The way forward with TA is to respond in the other person's mode - in this case, Parent - and then talk them down into reasonable Adult mode (or have a Parental argument, if the mood takes you!) A Parental response to her patronisation might be somewhat like "Sister, have you really not noticed it's the 21st century? You talk as though we were in Jane Austen novel! [indulgent chuckle]" If you can steer the resultant conversation to a DESC and agreement, you have done a marvellously Adult transaction :)
This is an essay, but I shall doggedly continue 
When BIL asks for a cuppa, your assertive response is something like "Not now, I'm finishing some work." If he's a machisto grown-up, he'll ask you how long you'll be. It's then up to you to decide whether to allow tea in forty minutes, or to say you can't make his tea right now and suggest he puts the kettle on. IT DOESN'T MATTER what he thinks of you, or what you think of them. All that matters is you taking your responsibility for your own self, and allowing them to take theirs.
I'm really curious to know whether this is any help? Small changes in the ways we interact with others can wreak tremendous changes in those relationships; the core point, always, is that you're OK. So are they. It's merely a matter of finding ways to make this clear :)
FWIW, I was elected to speak for my siblings at my psychopath father's funeral. I didn't say he was lovely. I told the truth, in an OK/OK way. I'm still very proud of this, and my speech was very well regarded. You don't have to pussyfoot, neither do you have to rage.