Grammar in this sentence--Genitive & 'whether

Andrew is my fiance's and my best friend and so must come to our wedding with two presents, one for me and one for my fiance, whether the present for me is inexpensive or not.

1) Do you think the sentence is grammatical?

2) I have used the possessive of 'fiance' because she has a separate friendship with Andrew. If it were a shared friendship, would I remove her possessive and keep mine: "...my fiance and my best friend..."?

3) Would it be more idiomatic or preferrable to write it as below, or do think it means more or less the same thing to the same effect?

Andrew is my fiance's and my best friend and so must come to our wedding with two presents, one for me and one for my fiance. Whether the present for me is inexpensive or not doesn't matter.'

Thank you