I love my wife's brother
Why do you love your wife's brother?
He has a great beard. He always keeps it looking nice and trim.
That must be some beard!  It's important that you don't act on the feelings, as you shouldn't get involved with someone else's spouse, and especially not your siblings!  That would cause a ton of drama!
There's no harm in saying you love someone like that, keep my statement in perspective.
If you're just making an innocent statement that's fine but if professing your love for your wife's brother, that's very awkward. Try to remember what your relationship is with him, he's your brother-in-law and anything beyond friendship would be a challenge for your family.