Perhaps your sister could visit YOU, instead? Then your dogs would be in YOUR house and your BIL could stay in a motel if dogs bother him?
I've been very lucky, I guess: all of my "significant others" have loved animals. It's kind of a "condition of the relationship" ... I don't think I could ever trust someone who didn't care for critters. My pets mean too much to me to attempt sharing my life with someone who couldn't learn to love them, too.