S.A.
Maybe have your husband mention to him that if he (the brother in law) is concerned about Zoey getting a cold, germs whatever it is from your daughter then instead of in the long run making daphne feel like she cant touch anything, like she has something wrong with her, or that she is not liked by them which after a period of time of doing this will affect her in one or more of these ways I am sure. Just have Daphne wash her hands or use sanitizer in front of him so he is not all freaked. I can understand the "germ" thing but that is why there are sanitizers out there. He has to learn to deal with it. It is up to the Parents to take care of that not give another child a complex because she is only 2 and does not have a clue to why he does not want her to touch anything of Zoeys! Once Zoey starts school what is he gonna do? They have sanitizers in the class rooms that they use often to help with the germs etc... he needs to find some ways to deal with this issue.
By the way I am a mom of 4, ages ranging 18-6 and also I also have (OCD) Obssessive Compulsive Disorder~ I am a Germ Freak!!!! I have the sanitizer hand washes, the hand wipes etc... always using them. I wipe our telephone down several times a day so I know there are ways to just deal with it as a parent and never make someone else feel like they are dirty or wrong! The issue is with me not them! Maybe this will help i dont know but good luck!
S.