It will always have to be them. Your stepchildren are jealous of you. But admit it, you're jealous of them, too. If you make it a battlefield, this is a battle you'll lose.
Corollary: "Wake me when it's over."
Rather than enduring the time you spend with his kids, enjoy it. They're never really going to go away, even if you stay under the radar. Intimacy may be a long time coming, but, like so many other situations in life, you've just got to put in the time. Granted, it's a complicated dynamic, but the Beatles were right: "The love you make is equal to the love you take." Or is it the other way around?