Just ban all adult aholes from your home.  And that includes your new wife if she is one too.  

My mom got with my stepdad when I was about 18. It was understood that I would respect him. Every time I didn’t (at the beginning) my mother checked me. Her parenting didn’t stop when I hit 18... she continues, even today, to teach. That’s what parents do. If your wife doesn’t ACT like a parent and train/teach her kids, you have to decide how much you want to interact with her side of the family. It is perfectly acceptable and downright logical to opt out of dealing with ANYONE who treats you poorly.

They most likely will not have anything to do with your son.  Major age difference, but should say hi, goodbye ect. They Should invite you for holidays ect.  You did not break up there parents ??? 

your wife and her children are not responsible for your ex wife abandoning you and your son. It's not their job to soothe his abandonment issues. Why did you decide to marry a woman who isn't interested in blending your son into her family? You chose to put your son into this and are now blaming adult strangers for not wanting to be chummy with a 10 year old? 

I am curious about what it is that the one does to be mean. What does your wife do when her child is mean to her husband?

That's too bad. I have 2 adult bios & 4 skids. My youngest bio really likes the kids. He recently said he feels bad for the little ones when BM ditches them not once but 3 times in a wknd she pushes her pick up time back til she finally says she's not coming. Since my ex did that to my sons when they were kids. I think my younger son feels a connection to them in that way. My oldest has no connection with them, he is somewhere between indifference and annoyed but he is polite & nive to them and my little skids look up to my big kids.

My bios live on their own so maybe that makes a difference. We dont see each other enough to annoy each other.

I hope they come around. Step sib rivalry is tough. They are prob jealous cuz he's so adorable!

You don't mention how long your DW and you were together prior to being married and what if any exposure your DS had to her adult kids.  On the face of it, it sounds like not very long.. and not much.

If that is the case then you need to try to view things from their point of view for a minute.  There are very few adults that are interested in hanging out and entertaining a 10 year old.  Now, obviously, they should be cordial to say hello.. and certainly not be "mean" but they aren't going to feel obligated or interested in entertaining your boy.. having conversations with him etc...  They are there to celebrate with their family and despite the fact that you married their mother.. they don't see you as their family.. you are their mom's husband.  Again.. they should be civil.. but if they want to spend their time catching up with each other.. that should be ok.  You might call it shunning.. but it may be more like disengaging from someone they didn't ask for in their lives.

So, what do you do to protect your son's feelings?  Well... if you two are being "shunned".. or left out.. interact with each other.  plan a game or activity or discussion for the two of you.  Or.. do you have any brothers or sisters with kids his age that could be invited?  Unfortunately, with all the adults around... it is going to be awkward and boring for a 10 year old.  He isn't going to be wanting to have a conversation with them about topics they might have interest in.. it just isn't a great mix for socializing.  So.. make sure he has a book.. computer game.. etc.. and after the meal etc.. he can excuse himself to his room to go "play".  If you want.. maybe you and he go outside to toss a football or something? 

Unfortunately, this dynamic of being awkward isn't just related to stepland.. but also the age of your kid.. the fact that he is not well known to these people.. and I don't know anything about your son.. maybe he is annoying or something.(no offense.. lots of 10 year olds are aggravating at times..lol). 

I know you want to protect him.. do that by paying attention to him and not forcing him to remain in the party area.. so he can go do his own thing... if the celebration is not on the actual holiday.. consider letting him have a friend over too

I feel your pain.  My SD are 27 and 30 - I have never seen such a level of dependance on Daddy.  I recently started practicing disengagement with them.  They didn't know what to do.  I took the control of their behavioral towards me and my bio sons out of their hands.  The 27 year old went to live with her mom in TX 5 years ago so she was here visiting.  They noticed the change when I practiced applying disengagement.  I was told that I ruined the 27 years olds vacation.  LOL - They ignore us anyway so I was surprised they noticed at all.  They were more bothered by not having the control anymore.  I spent more time with my boys.  My boys are older and in college at the time but they play football.  I spent far more time at football practices then I ever wanted to but it was better than being at the house.  I felt better being with the boys regardless. It is more than the difference female vs. male differences.  They are just nasty in comments etc., Take control of your time with your son and enjoy it!!!   

It sounds like the problem here is the expection that your only child who 10 years old will be embraced by decades older adult step siblings who have nothing in common with him.  Many times in intact bio families older sibling will have little interest in a younger ones. Also SM has already raised her kids and may not feel like jumping head first into your abandoned child's drama.  The kid may be the center of your world but the fact is that most everyone else doesn't really care if he's there or not. 

Also the two of you are the new ones, the outsiders, so ease into the family rather than expecting instant acceptance.