Wait a minute wait a minute. You need to explain how he is crashing your vacation. From the info you've provided it just sounds like you want this to be about you. Not your husband, his brother, or even your son. Now, if he planned his own trip to coincide with you guys, that would be a little messed up.

I think the best thing to do right now is to provide the hive mind with more background before people rush to judgement for you.