Hello, I am a step father to 3 children of my wife of almost 3 years. We have 2 boys, aged 5 and 7 and a daughter of 11 years.
The kids haven't really known their biological fathers at all, so I'm all they've got as a dad. The youngest especially has a strong bond with me.
The only problem is that he has a bad habit of defying me if he is in a bad mood or tired or something.

If he is disobedient around his mother, she will demand that he does what she asked or, if need be, shout at him and threaten to take something from him him or threaten to whoop him ( she and I have both done this in the past but nowadays we are avoiding the physical punishment) and he straighten's out with mild resistance.

If he is disobedient around me and I demand that he does what I ask, sometimes he defies me and just laughs or sometimes calls me names or will throw toys or mess something up. I will try to reason with him that acting this way will not get what he wants etc. But eventually I'll end up shouting and he's still not listening then his mother steps in and freaks out and starts yelling at me and then its pretty much over for the rest of the day between her and I. He still gets away with his defiance. I'm talking serious argument here : threats to leave me and all. He is manipulating me with his mothers intolerance of my shouting to get what his way.

If he just decides he wants to say no and she's not around to hear it and get on him about being disobedient then he pretty much has a get out of jail free card. I have one of 3 choices after he says no:

1. yell and threaten to whoop him or take away his video games or something, after which he would probably smile and laugh and say "no you won't", or start calling me names or laughing.

2. I could walk away and try to forget my own child blatantly defying me.

3. I could try and bargain with him and beg to try to get him to listen.

Option 1 : risk a massive argument and have my wife start threatening to leave me and calling me names (great 2 people I care about calling me names), son still doesn't have to do what I asked him to do

Option 2 : son gets away with absolutely no resistance

Option 3 : empowers him even more and reinforces his behavior.

Because my wife often yells and threatens him when he lies, or disobey's or talks back or acts out, he responds to that. But when I try, he knows that he will get away with it because he's been taught that I'm not allowed to discipline him like his mom. He's been taught that he doesn't need to listen to me unless mom is there too and that if he makes a big enough fuss and gets dad mad then he for sure won't have to do it.

The kids are so attached to their mother and they really trust her in the end no matter what, they will be with their mom. It doesn't matter if what I'm getting angry about is really valid, its the fact that I'm angry about it that dilutes the whole issue.

The real problem is that he doesn't listen to or respect me and he needs discipline from his dad when he acts up and his mom not to step in. She needs to step back and let me discipline him and then maybe some things would change.

She's hypocritical when it comes to parenting the kids. She expects me to be all good and patient but when its her turn she just shouts and threatens as if its going out of style. Its true that its not all the time she shouts.

She has a way with them. She's reinforced her bond as a dominant person to them. They know not to push it with her because they will get it if they push too far But when it comes to me they know if they really want to dance, moms gonna step in when I try and dance too. Constantly reinforcing that has eroded so much of their carnal respect for my dominance as a parent that they will never respect me like they should their dad.

I don't know how much more I can take.

We have a baby between us now that will be born soon and I couldn't imagine ruining my chance at being a father to my own flesh and blood child. Not to mention I do love my wife and children we have now very dearly. I have invested my soul into my family. I am just so frustrated at the dynamic between me and my son.