OP, As the eldest bahu, you are most evil but at the same time you have very prominent position in the extended family. Know that tradition gives you very prominent position in the family. If you want, you can boss your cosis around. After few years, when you are a seasoned bahu, your words will carry equal weight as of MIL. Writing this just FYI. The new cosis will always suffer less than you. So, don't feel bad for them hearing the childless taunt etc. About the gold, let MIL taunt cosis, no one has seen the future. Just don't give your opinion, in front of anyone. Keep the girls night out, that way it will keep the MIL in check, but at girls night out do not give your real opinion and any good topic- like gold etc, just let the co sis talk.