C.R.
I am a mother of 2 (age 9 and 10) from my first marriage and have remarried and now have 3 more, 2 boys from my husband's first marriage (ages 16 and 10) and he has a daughter from his second marriage (age 8). We have none together, cause we thought we had enough. When I met my husband he had custody of the boys and joint custody of his daughter. In addition to that, I have custody of my 2.
Everyday can seem like a battle, between disparaging comments about me from my ex and his first wife, and then let's not forget the hatred our 16 year old has for us, who has since gone to live with his mom, who has few rules and a much more "open" lifestyle for him.
I choose to see the good, I am fortunate enough to have the 4 youngest with us most times, and I get to stay home with them, and eat lunch with them and volunteer at their school. (The boy's mom didn't even know where her sons's schools were for a while).
I know when you hear enough, and you see the looks on the kid's faces, and you know what's being said, it's hard not to believe it too sometimes, but I know I am doing what's best for the kids, and the choices are hard sometimes, and the place of the "bad guy" since we have structure and rules in our home is not easy, but I never have to stoop to the other parent's level. All of our children will see things for what they are, be it now, or when they are older with their own children. They will know in their hearts and minds that this house is one of love and structure and hope, not one of tearing down other people to make things seem better for the moment.
Hold strong and love his children and yours all the same, even when it's hard, because you will sleep better each night knowing you are doing what's best. (and yes, I have to remind myself this daily, it's not easy).
My husband and I are even in therapy proactively, to prevent any communication breakdowns, and to faciliate communication with the kids when it's hard to find the right action or thing to say.
I know we are OK, and I hope you will find a place where you are too. Don't let their jealousy guide you, just love them all and be fair and even, they WILL appreciate it.