I’ve found conflicting instructions on how to use family words and I wondered which were the right ones.

Some say that titles like: okaasan, otousan, obaasan etc. are only to be used when talking about someone elses mother, father or grandmother.
Others say these are just a formal way of speaking to your family members depending on how close you are to them. If you were closer, you might say, kaachan, touchann or sobo instead.

So I’m a little confused. Could I call my grandmother obaasan, or would I in fact be ineffectually referring to someone else’s grandmother?

I hope you can help! Thanks for your time ^_^