I feel like I can't say anything to DH about his kids (17 and 20), without it turning into an argument and me being accused of hating/disliking them.
I treat them kindly and patiently, leave their dad to parent them but will sometimes point things out to him (privately) that I dont agree with.
E.g. SC1 has his own income and a very large amount of savings (a result from not being asked to contribute anything to household expenses). He'd broken something in the house, which would cost us minimum £200 to replace, yet DH wouldn't even ask him to pay it and says if he does and gets a refusal then it's fine because he "can't force him". In the meantime he still treats him like a child - pays for everything when they are out, buys him expensive Xmas gifts, expects no responsibility or anything from him.
I don't agree with this and told him so, but it only caused a fight.
It was my birthday recently, SC's weren't here but were invited to join us for a lovely dinner out. They did - but not even a card, nothing. Of course I know I'm not their mum and didn't expect much, but I can't imagine going to anyone's birthday and not hand them a card. DH saw that but didn't say a thing... I just felt really hurt as I teach my child these kind of things and for every one of DH's birthdays, I always check and make sure they have something for him, even if small (a card and chocolates usually). I'd be so embarrassed if they just showed up like this, especially at their ages.
Some days I really resent being in the position of a step parent, being unappreciated with a DH who either doesn't care or doesn't get it.