A non-disclosure agreement will NOT protect you. You need to patent before disclosing. Choose ONE invention, the best and patent it. Get it sold or licenced. Then go for the next. You should be doing the next prototype and getting it ready and so on.

Get with your inventors association and ask them about reliable angels. Keep ALL documentation secure, keep ALL records, note ALL conversations with date and time. Don't trust anybody to keep your unpatented invention secret.

Even a patent doesn't protect you unless you have money to litigate. That's how the world is.

There are many threads on this forum on the topic of patents etc. Have a read and you'll get an education. But definitely go to your inventors association where ever you are. They will clue you in big time.