The best thing I did for my marriage concerning the Skids was to ask my DH this one simple question.

I asked him if he's rather have his daughter love him for being a bad parent or have her hate him for being a good one.

It really put things into perspective for us.
I'm not being undermined.
SD8 is held accountable for behaviors more so now.
And it's a lot more fair to my 2 Bios and our son.

It's not 100% perfect and never will be but this helped tremendously.