These are all great questions. You do have to modify your movement with osteoporosis to minimize the risk of fracture. Here are some things I've learned:

~When bending (if you need to pick something off the floor), instead of curling your spine forward, bend deeply at the knees, keeping your back rod straight. Alternatively, you can do what they call the golfer's kick to pick something off the floor but that's a little trickier on balance. Hard to describe the movement but hopefully available on a search.
~Along those same lines, avoid crunches. Important to strengthen your core so you can do toe dips instead. Laying flat on your back you bring your legs to a table top position. Maintaining that table top, touch your toes to the floor. You can do this with both legs together or you can alternate legs (or do a bit of both as they strengthen differently).
~When getting out of bed, don't curl to sit up, roll over onto your side with knees bent, keeping your back straight push yourself up to sitting with your hands.
~When twisting or side bending, go gently and not to full range.
It's a bit of a learning curve and sadly, we have to think about it all the time to try and keep safe.