Nam

I think it's up to you.  Not necessary gold but maybe a small piece of jewelry for the sister in law.

I think lai si  would be a bit more than just two hundred?  Depends on your budget really

My sister in law told me years ahead that when I'm getting married, they will give me 1K each to help me out on my wedding.  As a bride-to-be, I think $300 lai si is good enough because I give out $100 to friend's wedding and more for close friend and family.  

It just personal preference.