Tell him if he has a problem with you, talk things out like an adult, or get on with his life. Just because you guys are siblings, it doesn't mean you have to be the Brady Bunch but while you are living under the same roof it is no fun for anybody living in hell. He sounds like a little kid trying to get to you, so he goes after your "toys".
I bet it has very little (if any), to do with the dogs.
The surest way to corrupt a youth is to instruct him to hold in higher esteem those who think alike, than those who think differently.-Friedrich Nietzsche Silence is golden, Duct Tape is silver.