My attempt is attached below. The constraints are fairly fixed but simple. There are some orange/brown G0 srfs to match and some cyan/blue G1 srfs to match:
Here’s another approach, but it’s not perfect. I used two rail sweep, trimmed that, then made a edge surface and matching that one. Next to it is a Quadremesh > SubD result 2023_03_08_5-Sided-Help.3dm (2.2 MB)