Replies to 'We Disagree On Punishment'

While my husband and I agree on discipline with our children, that is not the same with his sister and brother-in-law. While all of our children are the same age and all well disciplined, we keep experiencing problems with them overreacting and even bullying our eldest child during the 3 or 4 times we see them each year.  

Our inlaws and we couldn't be more different in our parenting styles. My husband and I are playful parents and enjoy being with our children while my inlaws are very serious people and openly mock my husband and I for playing kids music in our car and tell family members that we are overindulgent for buying our 2 1/2 and 4 year old sons certain toys like tricycles and a kid pool and taking them with us on family vacations (they go alone). 

During our most recent visit to my husband's parents' house, my son started to form teams with his other two cousins and younger brother. I stepped away to get a jacket and came back to find my son explaining to my 3-year-old nephew that he was on the same team with my younger son. While I smiled at my son's efforts to organize a soccer game, I overheard my brother-in-law snap at my son to "stop being mean". While I know my son isn't perfect and he can sometimes say things with the wrong tone of voice (he just turned 4, after all), this was a perfectly innocent comment on my son's part. Later, my mother-in-law gave all of her grandsons light sabers. During play, my nephew ran between my two sons while they were dueling and my son struck his cousin with the light saber. My nephew didn't seem to notice or care and kept running but my sister-in-law saw it, jumped out of her chair, and shreaked at my son for hurting her son. Her son started to cry then and my son ran over to apologize. She pulled her son away from my son, shot my son a mean look, and asked her son, "how did Alex hurt you?". My husband stepped up, apologized to his sister and explained that it was an accident. His sister backed down then but she hovered around her son the rest of the evening and my other sister-in-law overheard her tell her husband that my son was a tyrant and always hurting their son. Meanwhile, both of my sons get along famously with my husband's brother's daughter and their other friends and in fact, when he and his cousin are playing without my inlaws around, everyone gets along great too. It's only when my inlaws are there that there are problems. 

While these comments and overreactions don't seem to bother my son as nearly as much as it does me, I am concerned that I'm teaching my inlaws how to treat my son. I noticed during this last visit that the pattern may be spreading to my younger son who learned over to hug their 15-month-old daughter who was sitting besides him on the floor and again, my sister-in-law flew across the room to pick her baby up and away from my son. I fear that eventually, these snide comments will hurt my sons' feelings and I would prefer to stop it before it does. My husband usually lets these things slide and only occasionally steps in like the sword incident but I feel we need to be more assertive in stopping this behavior.  Am I overreacting or should I step in and start defending my son against his aunt and uncle?