Just a different perspective, as someone who is in the same/similar generation to your children (I'm nearly 29, am married and have a child now) and who probably did a lot of the same things you are describing not so long ago really.
First off, while I've only been the child in this scenario I can sympathetise (although not relate) and agree that some of these behaviours are a bit much and unreasonable for two adults. At 21 I was actually pretty horrible to my mother and on the one hand felt resentful of her interference in my life but on the other I expected her to drive me around, accommodate me during the summer between university terms, pay for expensive things when I needed them, fix problems I didn't know how to solve. I'm not proud of it now, of course, and have apologised for my more appalling behaviours.
I do wonder now what gave me that sense of entitlement. My mental health at 21 was terrible, mostly due to hugely traumatic events in my late teens, and I genuinely did need support, but I don't know that that explains it all. I think a fair amount of it came from being raised in an enormously privileged situation in which I never really had to be responsible for myself. I don't mean that I wasn't held accountable for my actions as a teenager or that I never had to work hard - I actually worked like a Trojan at school. It was just that whatever I couldn't do myself, my mum had always tried to help me with or make happen for me. I think that involvement from a parent is normal, but perhaps the trend now is that "pulling away" of the parents is happening later and later. It then comes as more of a shock to the adult children, who do genuinely want to take responsibility for their lives, but who haven't yet acquired the necessary maturity to do so.
Lots of people point to "coddling" or "lack of resilience" being at fault for this sort of behaviour, but I'm not sure it's as simple as that. Yes, many of us had far more help and involvement from our parents than previous generations, but fundamentally we are living in a different world which has different requirements and expectations for young people. I don't think it's fair just to blame parents for this or to brand an entire generation "snowflakes" just because they are struggling.
In any case, I think your children will grow out of this eventually. You don't have to rip the rug out from them, but perhaps as others have suggested you can gradually take a more hands-off listening approach. And yes, when demands get unreasonable it is okay to say so. It's a buzzword but I think "boundaries" are important to establish together. Having clear expectations of each other can really help establish what is and isn't okay now that they are adults.