Venting

So my husband's uncle brought his niece and nephew over . the girl is a little over 1 and my son is 3. I was sitting in the living room when she was playing with his little light so i told my son to grab it from her so then the uncle was like "give it back, I dont want him hitting you again for it" all passive aggressive and my husbands brother slapped my sons hand! I was so shook like no one can spank my son except me, I'm 39 weeks pregnant so my emotions ya know, I just brought my son to the room and started crying like wtf. Just to add that my husband adopted my son a couple months ago so the now uncle I feel he has no right to that especially since he or i didnt see him "hit" the little girl . i feel that the uncle just said that all dramatically too just because my husbands mom, dad and brother was in the room. and hes always rude to me so obviously he doesn't care much for me much . I'm new to this family for the past year so . this situation just made me feel so upset