I think it is also up to your DW, if she wants you to help and wants you involved in raisen her kids then she should also be supportive of you. Of course you should be in control of what goes on in your (your and your wife's) house and that can be achieved in many ways, one way is for you to set limits and boundaries and she can enforce and deal with issues that may arise within those boundaries (disengaging), the other is for both of you to actively seek to raise and deal with any issue that arises in the house. You should talk to your wife and decide what is best for you making sure that if you decide on the first way you may feel like an ostrich but need to let her handle thing her own way, and if you decide to go the second way then she needs to be supportive of your decisions (and you of her) and be a single front in raising the kids.

My advice is talk to your wife, you are feeling left out most likely because she is dealing things her own way and you feel ignored and put aside. If she wants to deal things this way (if she really thinks is the best for her kids) then by setting your limits and disengaging from parenting is the way you are supporting her. 

Sadly, you just have to be ostrich with your head in the sand. I'm learning the hard way. I never in a million years thought it would be this way....that in MY OWN home I would feel like I don't have control. It is so hard. I have recently had to put my head deep in the sand and IGNMORE my grown ass 16 year old step daughter playing hide and seek behind the curtains in my house....tugging on them causing the rod to come looose from the screw.....16 years old....yes you read that right. DH seems to think it's cute and funny.....while I'm literally plotting my divorce because I can't take it....these kids 16 and 11 climb on the furniture and just run around like animals screaming in my house.....I want to freak out. But poor poor guilty daddy can't bare the thought to ever correct the poor poor kids.