It would be a good move to have some fun with them all in the evenings including your partner, you do sound jealous of the attention she gives her children, they need that attention and so do you, make sure you and your partner spend quality time alone, but also you could join in with them in the evenings and weekends, Games and Fun, all go for walks ,bike rides, play Monopoly, or scrabble. You are feeling left out so dont let your self be , you can change the dynamics here, Good Luck