The door jamb should have been wider, probably a special order. I had the same problem, including the concrete porch pulling away. I was able to extend the jamb and I don't think anyone notices it. I had to chip out the concrete porch to get the new door to fit. Just so it didn't look like the porch was patched a new porch project was initiated. That was pricey but makes the house POP. The door salesman never asked any questions other than "door swing direction." If he had asked the question about jamb width I would have jumped at the chance to make it right without the "fixes". The porch material salesman was a real pro. Spent a lot of time with him and he sold me all the materials from base, new sidewalk pavers, step treads, porch slabs, cap blocks, adhesives, etc. There is so much to learn as a DIYer. Methods and materials are always changing. I wish you well with your project. I think I would use a PVC trim piece where the brick molding meets the brick. Check with the door manufacturer. You may be able to remove the brick molding and replace with a different size.