From prior posts, it seems that your SS is somewhat immature.. probably, in part, due to the fact that your wife probably likes him being her "little baby boy"... and she has encouraged this dependent nature in him.    it's not your SS's fault.. he is behaving as he was encouraged and taught to do..  I do feel that perhaps in a few years when peer pressure kicks in more that it will be less "cool" to hang with mom and sister exclusively.. but that doesn't necessarily resolve things now.. it will be a wait and see..   

The real issue is your wife wants and likes this behavior.. she may "appear" annoyed at times over it.. but it makes her feel loved and needed.. so.... why would she change it.  Sure, it's not super healthy. but again I've said it before.. he is 9 not 19.. time may be your friend here.. he is unlikely to be totally attached to her forever..he may mature as he sees his peers also pull away from their mommies hugs and tease him for his.

When he interrupts a conversation, calmly tell him that the grownups are talking and to wait his turn. You can also tell him that the remark/comment/question was not destined for him, (again) the grownups are talking.  All of this is well within your rights as an adult. Also, as your wife apparently doesn't notice these things, this will bring every incident to her notice.

You have a voice.

Walk away. And when she asks why you decided to go back to the room, read, take a walk, etc tell her the truth.

"Honey I walk away when Skippy Doodle gets his 'look at me, look at me, look at meeeeeee' on. I figure you must enjoy it  when he acts like a child 1/3 his age, and don't seem to notice the looks from others when he embarasses himself and you. I could call him out on it but you seem to like it and I love you  so I leave you to it. He's your child and I do not want to impede your joy. "

Hit the nail on the head. Your DW iis encouraging this behavior.  She wants it to continue.  You have a DW problem.  A problem I don't have answers for.  Maybe seeing some one for help. A third party may show DW her errors.  Or DW will that the therapist nuts.  And will refuse to see them . 
The answer for being d|srecepted in a relationship is the exit plan.  What is your choice,,  being together and knieing this SS cra$ is not going to change. Only going to get worst.  SS will have no friends. And will be home  24/7/365.  Or looking for someone else who respects you. What's hard. 
'TWO  SS is becoming the alpha man of relationship. Control your life.  That's impossible to live like that. Not going on vacation with DW doesn't solve anything.  All that does is tell them they win. 

I know the kid is 9 but unless his mom teaches him how to behave maturely (at an age appropriate level of course) then it could continue to adulthood and beyond. 
 

However, trying to tell these Disneyland parents how to more effectively parent their kids will be an uphill battle. 
 

You can be more patient, explain your stance and hope she comes to her senses and/or ignore/"disappear" when you see the behavior occur. 
 

I don't think this is divorce/separation worthy ... yet ... but frequently disagreeing over parenting styles of the kids can be a major source of contention that can lead to end of relationships if both parties don't attempt to get close to the same page/come up with a solution that works for everyone 

This is just bad parenting..  Do she want her kid to grow up the joke of his school.  Having no friends, no activity to do.   This kid must grow,  do thing on his own. Learn about life,  how to handle life.  9 yo handle life on a 9nyo level. To go on to a 10 yo leaves to   .......   

By abandoning your marital position to a hell spawn of a failed family coupling you are facilitating and even amplifying the issue.

Start immediately with zero tolerance and climbing his toxic kid ass when he perpetrates that crap in front of his mommy since she does not have the parental spine, is a failure as an adult, as your mate, and has no testicular fortitude in holding her spawn to behavioral standards.

When he interrupts tell him to leave the table immediately and go to his room as rude children have no place in adult conversations.  There is a long history of successful parenting under the "Kids are to be seen and not heard" model.

I would not tolerate this crap if I were you. 

Fortunately for me as a StepDad married to a biomom, we landed very eary in our marriage that as equity life partners we were also equity parents to any children in our marriage regardless of kid biology.  Our son, my former SS who asked me to adopt him when he was 22, was raised with very well defined standards of behavior and standards of performance starting not long after his mom and married the week before he turned 2yo.

So, if your mate won't step up and get it done before you have too, then you do it while giving both mommy and her ill behaved spawn clarity that standards are in place and will be enforced whether either of them like it or not.

IMHO of course.

Good luck.

By abandoning your marital position to a hell spawn of a failed family coupling you are facilitating and even amplifying the issue.

Start immediately with zero tolerance and climbing his toxic kid ass when he perpetrates that crap in front of his mommy since she does not have the parental spine, is a failure as an adult, as your mate, and has no testicular fortitude in holding her spawn to behavioral standards.

When he interrupts tell him to leave the table immediately and go to his room as rude children have no place in adult conversations.  There is a long history of successful parenting under the "Kids are to be seen and not heard" model.

I would not tolerate this crap if I were you. 

Fortunately for me as a StepDad married to a biomom, we landed very eary in our marriage that as equity life partners we were also equity parents to any children in our marriage regardless of kid biology.  Our son, my former SS who asked me to adopt him when he was 22, was raised with very well defined standards of behavior and standards of performance starting not long after his mom and married the week before he turned 2yo.

So, if your mate won't step up and get it done before you have too, then you do it while giving both mommy and her ill behaved spawn clarity that standards are in place and will be enforced whether either of them like it or not.

IMHO of course.

Good luck.