Learn English – Pronouns: when to use possessive vs reflexive

Your example in number 2 is an incorrect use of the intensive "myself". The intensive pronoun is an emphatic, redundant pronoun. In your example, an actual object is needed for the prepositional phrase "for [object]" , so only object-pronouns (like "me") are appropriate.

You would use the intensive pronoun like this:

I, myself, am responsible for the company's success.

Note that in this example, without the intensive, emphatic pronoun, the sentence remains intact "I am responsible for the company's success."

I think that this is confusing because you're using your and my when we already have a word our which would normally be preferred. For this reason the sentence is a little awkward, because it's not really clear why the writer has decided to not use our here.

If you want to use your and my for emphasis, which you certainly could do, then it would be a good idea to use the marker both here to highlight this:

Both your and my grandparents grew up listening to this piece of music.

This sounds perfectly natural and correct.

With regards to yours and mine, this is ungrammatical. The reason for this is that in modern English we never use mine or yours when there is a following noun.

• It's my elephant.
• It's mine.
• *It's mine elephant. (ungrammatical in modern English)

I think your last sentence is a bit awkward because there doesn't seem to be any benefit in terms of meaning or effect for using such a complex construction when our grandparents would seem to do the same job.