Me and dsis are close, although we see each other rarely (other end of the country). We go through stages of phoning regularly, and will talk for a couple of hours-or until the battery goes. 
If she phoned and said she had a crisis could I come, I'd be on the train in a twinkle and I know that she, barring work commitments, would be the same.
We're very different personalities though. I was always the girlie girl wearing pink, playing dolls etc. She would be found in muddy jeans half way up a tree. 
I'm not close to my db, and looking back it is my parents' fault. He was the youngest, and the most difficult. When he was 18yo, my dm said in telling me something was, as usual, revolving around him, "you have to make allowances, he's going through a difficult time" to which I turned round and pointed out she'd said this for 10 years. About 15 years later she still says this to excuse revolving round him.
The thing is I think four fold problem.
- He is much more likely to make a fuss if he didn't get his way than me. So there would be times I'd be pushed back, and pushed back and pushed back because at each stage it was easier for them to ask me to back down than tell him he had to. Sometimes I didn't mind, other times I was really upset, but if I said so often I was made to feel that I was being mean. And it still went his way.
- Dm could see that he struggled/s socially. He really does. So I think she felt that I would have friends etc. and he would find life harder, and tried to make up for it, so she felt I shouldn't complain if things at home revolved round him as I could go out with friends that he didn't have.
Now I am very shy and find making friends difficult, so I found this really hard as I put a lot of effort into this. So I felt I was being penalised for putting this effort in.
- Because they would never correct him, he didn't learn. He has learnt a little now in the real world, but he takes any criticism either as not valid or that they've taken a dislike to him, not something to learn from. Dp tend to encourage that feeling too.
- They encouraged him to have/do the same things as me, and always compared us with him favourably even when it was clear (looking back) I was better. He's 3 years younger, so I always had this champing on my heels feeling.
If I give an example of the musical instrument we both player (violin). He's tone deaf, and took 10 years (and 4 attempts) to pass grade 1, so he wasn't good. Dm would talk about it along the lines of "oh yes DeWee and DeBro both play. DeWee finds the tuning easier, but DeBro has really good bowing technique and style, he's got such good control, it's beautiful to see..."
Other than looking back, dm wouldn't know that sort of thing anyway, but then people got the impression he was much better.
Dm was aware I was better (grade 3 in 2 years) so she over compensated.
There were also things that he took for granted that me and dsis would have only dreamed of. Shop bought cakes were one thing. A shop bought cake for me and dsis was one chelsea bun, divided into 5 and us all have officially one piece each (but usually dm gave at least half hers to dbro) The first time I came back visiting from university dbro had a huge strop. Dm had bought a packet of 6 donuts. His strop: well obviously I would expect one so he was now only going to have 4 (df expecting one too) rather than his usual 5. Yes, you've guessed it, me and df were only given half each. 
We were late for my wedding rehearsal because we stopped for a quick snack on the way-and dbr insisted on having a full 3 course meal. Taking lunch to dsis when her baby was born, we were well over an hour late because just as dm said we would leave he decided he wanted to have a shower...
Most of these things are dp fault. Not because they favoured him. But because they were afraid of the fall out if they didn't pander to him. Result is that he still struggles socially because if he's never been told then how doesn he know?
Dm's often would respond with a phase, if we said things like "just go and leave him behind then he won't decide to have a shower/change his clothes/have something to eat etc. before we left very late: She'd say "I can't leave him behind. he's my son!" However I suspect if she'd done it once age 13/14 he'd probably have not done it since, so ti would have been much more loving as he now can't understand people that don't make those allowances for him.