Children

I need some honest opinions & advice regarding alcohol related family issue.

My father died at 57 from complications of alcoholism. I have been married 27 years & have 4 kids. My oldest was dx with alcohol addiction at 16. He was arrested 3 times for fighting and ended up in prison for 2 years @ age of 17 4 felony battery! From the day I learned my son was drinking/doing drugs, our family got therepy. Indiv, and family sessions. With love & support from God, my mom, and dear friends, we came thru that painful time! That son is 25, married and doing well. My other son (24) has also had alcohol related issues. Not as serious, but he has also been dx with alcohol abuse. We have not had alcohol in our home for 13 years. My husbands family can't have a gathering without it! Now that 3 of my kids are over 21, one of our brother in laws constantly encourages them 2 drink ! He pulls out shots etc at family events (where young kids are wittness to this b-I-l's very DRUNK behavior). He even called & sent text messages to my daugher weeks before her 21st birthday saying stupid things about partying and how many days were left till the big day! He is 48 years old! I've tried to explain our feelings regarding alcohol to them (watching my dad die, my son go to prison, etc) and also asked them to see this from our point of view. To ask them to try and understand what we've been thru. We don't tell them not to drink or not to serve alcohol at their parties. We know our kids are adults and make their own choices. We do think it is acceptable to HOPE that as Aunt's and Uncles that they would want to help and support their nephews...not try to encourage them to drink when their futures could be put at risk! The response I got was 'alcohol may have been the root of all evil for you, but that's not the case with our families. Stop making us feel guilty for having fun. Don't blame me for the poor choices your children have made. They say I AM Rediculous! Am I? Or, are they?
Is it acceptable for me to refuse to attend family events at this specific sister's home?