I have not heard of sailers welding the frame... somehow this might be difficult to weld the bars to the cast aluminum corner castings. Especially the problem that your pics show could not be fixed by welding since the heat involved in the welding process would cause damage to the hulls. (IMO)
Glueing the frame with epoxi seems to be pretty common. Search the forum and the rest of the web for How to instructions - there are many - some even with pics.
Useing epoxi is IMO kind of hard core and difficult to reverse, especially if it includes the pylon/cornercasting joint.
As a first attempt I would recommend shiming. First seperate the hulls from the frame - should be easy since it seems to fall apart there anyway. Check for corrosion. Also check the holes for the bolt (WS 19)in the corner casting/pylon conection - those might be oval. Also check the bolts (WS 19mm) that tighen this particular joint. My Hobie (85) came with wite plasic nuts, which three ot them had cracked. Try to messure the gap in your joint by sticking some kind of scrap sheet metall in it. Then cut and bend some shims out of the right size aluminum sheetmetall. The
shiming should not take to long; it will be reversible; and it should not cost more than $10.00