Are all brothers the same?

So I have 2 brothers, and we are all very different. Over the years I have been talking with other people who are in a family with two siblings and the results seem very similar (more so with all boys/girls than with mixed sex siblings). My theory is that the oldest child will generally be the most responsible one, the middle child will be the most independant, and the youngest will be the most emotional.
Would you agree?

Is it good to live with a family member?

My brother and I used to fight a lot when we were kids, but now we both are short of money and looking for a roommate. We get along ok now, but I don't want to risk the good relationship we have. What is your experience?

Do I tell my brother his new GF is a dud?

My brother recently met a girl through internet dating after going through some hard times after a breakup a few years back. He has done so much to get himself back to good physical and mental health and starting a new career, I am so proud of him. However, he has just moved in with a new girl, who he says is great. But, I have noticed that he has started drinking and smoking again with her, not much, but a bit. Also, they never show up anywhere when they are supposed to, and don't even call to let us know. When we go to their house, he will not let us in as he is embarrassed because she does not clean, cook, or do laundry and he works all day. The house is a mess, and I know it is her and not him, because he is over 30 and has never lived like that that. I think this girl might be a bad influence, but my brother seems happy, do I say something?

I don't want to get my sister a Christmas present

So, my relationship with my younger sister (she's 22 and I'm 25) has never been great but recently it's been an absolute nightmare. The last time she texted me was on my 23rd birthday asking to borrow my ID so she could get into a bar, and the last time we spoke in person she told me to "F*ck off." My parents have always tried to push us together and force us to have a relationship, but it just doesn't seem to be in the cards for us. We're all getting together for Christmas this year and it's expected that we all get each other gifts, but I really don't want to get anything for my sister. She has a 6-year-old daughter, so I'm thinking I'll get them a gift that they can enjoy together as a compromise, but it still makes me a little salty to get her anything at all.

Wedding present a free vacation?

We flew my SIL and her fiancee across country to meet him before their wedding. Plane tickets, guest bedroom, tours of fun places around our home, and took them to wine country for the day. Can we skip a wedding gift?