I understand the best mix is a sociopath an a borderline though it always ends badly ( very ) for the borderline
Indeed. Sociopath is the apex predator in the cluster B pantheon. None of the borderlines manipulation will have any effect on the sociopath (who has no emotions to exploit) and the sociopath will exploit the BPD abandonment fears mercilessly.
Sadly many pwBPD are attracted to sociopaths.
NPD and Bpd has a dynamic to it which seems to hold together well.
I can't see two BPD having any stability to hold together long term.
HPD and BPD would be probably the most insane combination you could get.