Hi Sharif, probably the easiest method is to do that outside first for both pieces.

I mean generate 2 non-hollow pieces and boolean union those first:



That gets the outside formed. Now to clear out the insides, in one direction that can be done by boolean difference with this inner curve:



And to clear out the other direction, make a mitered one-rail sweep of this inner curve and use that object as the cutting object in boolean difference:



- Michael