Extended Family Divorces

My brother and his wife are getting a divorce.  My kids are having a hard time understanding the changes that are coming. 

We have a vacation planned to our home state soon and we will be seeing my brother.  We won't be seeing my sister-in-law and the kids don't understand why.  They think we should be able to see my brother on one day and their aunt on another while we sit around outside around the outdoor fireplaces and visit.  My niece will be there for part of our vacation but then it is her mom's time so she'll miss the birthday party.  Trying to explain why cousins can't spend the whole time together wasn't fun.  It opens up insecurities and fears in them that my husband and I could divorce one day and they'll be in the same situation.  It's scary for them because they realize that it can happen to anybody.