Need advice from Step Fathers/Fathers please

I am a stepdad and a dad both, and I can tell you that sometimes there is no such thing as a "good stepdad"
Your great until you disagree with them, then it's usually on to mom to get "stepdad" to do what they want.

My youngest (my wife's biological daughter) told me one day a long time ago that if I didn't put her down she was going to throw up on me.
I told her to go right ahead because I would just go get a ziploc bag and save it, and that's what she would get for breakfast the next morning.

Gross I know, but she never threatened me like that again.
When they throw tantrums you just have to tell them they are acting rediculous blow it off.
Walk away shaking your head, and even letting them think you think it's kinda funny.
That really pisses em off, and then they learn that it does no good to throw a tantrum in the first place.
Tantrums only happen because they worked at some point, and they are trying it again.

Obviously when he asks and it was his idea, do it if you can if it is a reasonable request at the time.
This let's im know you would if it was an ok time, but sometimes it's not such a good time and that's just the way it is.

Also, times when you ask him to do something and he does it praise him for not throwing a tantrum.
He may have not even considered it at the moment, but it lets him know you appreciate it when he does not.

You would be shocked at how fast that last one works.

Then the younger one will see this and learn it for himself, and you won't have to go through it with him too. :-)
The way things are going now, you will I gaurantee it. (because he see's that it works for the older one)