Hello chezRon,

I believe we need more information... unless trouble with these plants in particular is common. I wouldn't know, not being much of a cactus guy. Just a partial cactus guy, like 6% cactus. It looks like you're in southern CA but we don't know your growing conditions - light, soil, watering schedule. If you have 70 cactus in pots, I assume you have some strong outdoor growing light. What have you tried with your Rebutias and Mammilarias? Have you tried different light levels? Have you been watering during the winter? What's your soil like? Low light and too much water in the cold season is more than some cacti will tolerate.

Disclaimer: I do not and have not ever owned either of the plants in question.