I am not a regular poster but for all is worth, this is my take on the issue. I think your situation is very complex, but in itself, not that unworkable at all. The problem you are facing is that you've gone totally the wrong way about it by deciding to get married before dealing with all the issues with time. You now face the reality that you can't all adjust to the situation quickly, but because you are married, there is now a seemingly urgency to sorting it all out.
It is totally natural to feel anxious about sharing your home. My OH was also massively anxious about it. Slightly different situation and reasons for doing so, but ultimately, he felt very much like you and yes, the first months... years.... were tough as we adjusted, often not in the most harmonious way. The insecurities on both sides came out in very meaningless ways, but it was our way we both coped with our adjusting to relinquishing some of the control we had built, successfully, for many years previously. I can assure that my OH was as nervous as you about us 'invading' his home (although of course he never said it directly!). Well 3 years on, he is the one who asked me very seriously how I would feel about moving out because suddenly, he decided that his perfect house wasn't so perfect, and ironically, it's me who is now settled and quite happy to stay (we compromised, we'll move in a a few years).
I could apply the same dynamics to adjusting to step children, money etc... The point is that all this takes a lot of time, conflict and in our case, it was indeed our deep seeded love that took us through it all and saw us coming on the other side happier than we've ever been.
The reality is, it just won't happen until you make the plunge and accept that you are about to face months, maybe years or rollercoaster. That's the commitment you made by deciding to marry (or else I really don't know why you would have agreed to go ahead with it). As said, would have been so much easier to have got married after the ride (as OH and I did), but it is too late now.
Remember that your fears and anxieties doesn't justify your choices though and you won't make it work unless you start to gradually let go of the control. I wish you good luck.