Disney does vow renewals, basically the same procedure as first time weddings.
Getting a dress size cut in half, will truly alter the dress and it's usually not an improvement. Unless you are doing it for sentimental reasons, I would get a new dress. You are not the woman you were 10 years ago, new person, new dress.
For your last question there is no right answer to this, it really differs per family what is right for you. You will have to make a decision and only you can make it. Were both these people at your wedding?
I am of the opinion that weddings and vow renewals should be about the couple and their wants & needs. It's nice to want to please everyone, but it is you want to renew your vows. Not the family members, they are not paying for this.
But you say you love the family member back home, you don't say that about the local family member, if you want to please one of them, please the one you love more.