Hi I see PaQ already solved this,

Anyways, I made an attempt using Rhino, and it seems to work with Curvature continuity on one side and tangency/nearly curvature in the "inner bend"





The inner bend curve is split in the middle, at the kink in the top curves. It looks like the "swx" patch isn't flat at the top, a thing one would sometimes want.
This one is at least flat at the top.




The control points:




Interesting problem and typically difficult .) I tried T-splines on it, but it seems to give a melting effect, yeah. But I may not have found the optimal way in TS yet.

Regards,
Fredrik