False. Some bacteria foreign to the body are deadly pathogens. Tuberculosis, for example, is an airborne bacteria that is fatal.
True. However, as I said, the good bacteria regrows in your body.
False to the former, true to the latter, but good hygiene and sanitary practices are something we were taught at an early age in school. Those things (good hygiene and sanitary habits) are not directly the result of having relatives in the medical field, though it certainly helps to reinforce the good habits.
That's not what results in osteoporosis, but we're all free to believe what we like. Your bones, like your muscles, atrophy and shrink with age. Of course, reduced mineral calcium and vitamin D levels in your bones are significant contributors.
This, to me, is quite interesting and curious, but not for the reasons you might think. You're mixing truths and falsehoods here, albeit likely unintentionally. Normally, I'd dismiss wild beliefs, like flat earth, because it causes no real harm to anyone else for those who hold that belief. But believing things like, "all bacteria are good for you," and then not washing your hands can have very detrimental effects and bring about direct harm to others, if, say, you work in the food industry in the kitchen or work in the medical field.