Either that or I am an unchaitable grinch who has no idea of what parental responsibility entails...I'm not sue.
Back story. My 28 yr old sister works abroad a lot, 3 to 4 months away and then 1 to 2 months home. When she is home she lives rent free in the annexe of my parents' home. She is a little, temperamental, demanding, whatever the word and is the doyenne of the family. I have a little lingering resentment that would make this thread far too long so I shan't go into it!
Anyway, in the last few months she has decided she wants to buy a house, and is sick of being with my parents. (Who while very loving, can be quite difficult.) To do this she needs a deposit of circa £25k from my parents, this is fine as I had the same a few years back. (Mostly gone since housing crash but I still have the flat.) As she is away, she enlisted my parents to help when she had an offer in on a place and needed help chasing people etc. That fell through, but the seed has been sown and now they are busier than she is,. shortlisting properties (she has full internet and phone access, earns a very good salary with no overheads and works shifts so has time and funds to sort herself), speaking to agents, liaising with owners etc etc. They are stressed about it as they refuse to aknowledge that she is an adult.
My mum was meant to be coming to my area (about 2 hr journey) tomorrow for a medical appointment and to see me and DD, we haven't seen her in a few weeks. Yet this eve she phoned to say she was putting it on hold because my sister had an offer refused on a property and so may decide she wants to go home on Friday morning to see another property. I didn't think anything of it (changing plans for DSIS is the norm) until I realised the house is a 5 min walk from the public transport she'll be using. I asked mum why DSIS couldn't just walk instead of requiring my mum to drive for 15 mins, wait, collect her, drive her 2 mins to house, wait (if she was allowed to view as well her opinion would not be welcome), drive the 2 mins back to transport then 15 mins home again. I was told that DSIS would probably be in a rush and it might rain. I am also meant to be seeing DSIS for lunch on Friday (an hour's drive but I had the summons) but of course that may not happen if it is all too stressful, but mum is sure she'll let me know on Friday. 
I did point out fairly forcibly that DSIS is 28, and capable of soting herself out. That I didn't get the rush/panic, and that mum and dad were not doing he any favours by perpetuating this behaviour. Apparently if they try to have words she 'makes their life hell'. Again I pointed out that that doesn't make her right, they are the parents and should stand up for themselves.
I mentioned this to DH and he was put out on my behalf that all plans to see me and their beloved DGD (I will get the 'oh I haven't seen her in so long' nest week, guaranteed) go out of the window on the offchance that my sister might need a lift 2 minutes up the road the following day, but this side of things hadn't really occurred to me as I am so used to my sister's requirements being put first.
Phew! Anyway. That was really long, but AIBU in thinking that they are far too involved and my sister needs to pull her finger out?