I'm not a panther gecko breeder. With my leopard geckos, at a certain point the females either stop ovulating and laying, or lay only infertile eggs. What I have heard about panther geckos is that they are very prolific and often "lay themselves to death" so I"m impressed that yours have gone for 6 years. I would assume that you'd have the most success keeping them healthy by removing the male.
Aliza