Definitely should be 大姐和二姐。 You should be very careful about the word '小姐' and try not to use it in any circumstances, especially to a girl~~~because it has a differently meaning in China.

平时我们说 我应该叫我爸爸的弟弟什么

You should just move on, trust yourself, be a confident woman, make him regret.

You can try to turst your best friend and see what happened.

central business district

Hi Beth, I don't think the tone will change much when you these two structures, basically the sentences with these two structures should be followed by question marks, so i think they both should have up tone(the second tone). About when to use 否' instead of '...不....' structure, i think '能不能' is more oral, like people would use that when they chating, and '能否' is more formal, normally they just be used in articles. But both the structures are frequently used i think, you can use both of them in normal life, they just have slightly differences.

I didn't feel it in Australia, are you in Japan?