Joanna Krupa -- Wants To Grill Other Housewives About Vagina Fish Comment

Joanna Krupa is dragging several other Beverly Hills 'Housewives' into her defamation lawsuit against Brandi Glanville, TMZ has learned.

Joanna's lawyer fired off a letter requesting 4-hour sit-downs with Lisa Vanderpump, Yolanda Foster and Yolanda's ex-husband Mohamed Hadid. Brandi has said she only repeated the "smelly vagina" insult from comments she heard from Lisa, Yolanda and Mohamed.

It does raise the issue ... why didn't Joanna sue the trio, in addition to Brandi, who blasted the insult on "Watch What Happens Live."