My paternal grandmother and mother both seem to have osteoporosis because they have major lower back issues. I’m only 18, but I’ve been having lower back pains too. I thought it was because I danced too much and over-worked my hips and back (hip-hop, salsa, krump, etc.), but now I see I run the risk of having osteoporosis too. What should I do?

There are many causes to low back pain. I wouldn’t rate Osteoporosis particularly highly unless the vertebral bodies have started to collapse increasing the AP curve changing the muscle balance.
Please don’t self diagnose this condition.
The only way you can tell osteoporosis in the early onset is with bone density scans.

Diet and lifestyle are major factors in preventing osteoporosis.

A diet too rich in protein and sugar is very damaging to bone health as is a very sedentary lifestyle (and having babies when you have a gynae age of less than 4. Your Gynae age is calculated by the age you are when you first menstruate. A girl aged 14 who started menstruating at 12 and a girl of 16 who started menstruating at 14 both have a gynae age of 2). A diet deficient in Calcium is also damaging to bone health.

If hip hop dancers are prone to Osteoporosis I suspects its because they are undernourished rather than because of their activity.
I treated a lot of dancers when i practiced in the UK as the clinic I worked in had a contract with a dance school. They virtually all had eating disorders and were osteoporosis waiting to happen.

I suspect your low back pain is probably because you have a deep lumbar curve if you do a lot of dancing.