What exercises are safe for someone with spinal stenosis (L2, L3), spondylolisthesis, AND osteopenia?

Can you answer B.Slippers’s question about Osteoporosis?:

I know spinal flexion is good for relieving spinal pressure due to stenosis, but I understand it’s dangerous for someone with osteopenia because it can cause fractures. I’m interested in exercises that will keep my core muscles strong.

Bone Health And Osteoporosis