Am I The Asshole?

My SisterInLaw removed my niece and nephew from my table at my daughters wedding. I am MOB and went to get a couple glasses of wine for my guest and myself while all the guests were looking for their assigned tables. I was gone maybe 15 minutes. When I arrived back at my table, I found that my niece, whom I'm very close to and had travelled 2K miles for the wedding, and her brother, my nephew, were REMOVED from my table and in their places were a SisterInLaw (whom I hate) and my brother (whom I love) and my SisterInLaw's brother and wife! I politely asked them to leave and return to their own tables. I made clear that I was not happy with her rearranging my table! My table was hand picked people with whom I wanted there, and assigned by my new Son In Law. Name tags were at places everywhere, at every table. SisterInLaw knew what she was doing was wrong! I asked several times in a stern voice and looked to my other sibs for backup! Nothing from the sibs! So I then shut up because I didn't want to make a scene and ruin the day for my daughter, who's table was right behind me. This happened 4 years ago and still pisses me off!