Congrats on taking a big step! My only advice comes from having been a stepkid--but I would say that the best thing my stepparents did was to leave all major discipline and decisions to my parents. They were there as concerned adults in my life, and they would reinforce their personal boundaries the same way you would with a friend (ie: you can't make a huge mess and leave it because that makes it hard for me to make dinner) but when it came to big issues (grades, staying out too late, money) it was a conversation for me and my actual parent, and they let us talk it out instead of getting too involved. I think it depends a lot on the age of the kids, but in my case, I have a great relationship with both of my stepmoms, and i think it's because they always made it clear that they were there to be a partner to my parent, and a part of my life, but not to control me. That and being fair to everyone regardless of whose kid they are, and I think you'll do well!
And so are the boys!