1) I doubt this is bullying. It sounds like kids with no adult guidance from either you (who knows what is going on) or Mom, who may or may not.
2) Even with adult guidance, they're reaching age levels where it could be very difficult (a 3 year gap is sometimes peer & sometimes 2 totally different worlds.)
1+2) With no adult guidance & 2 totally different developmental stages (little kid & preadolescent / puberty) ... There are GOING to be problems.
This is the grown ups fault, here. Period.
Kids push boundaries.
Kids don't KNOW boundaries.
Kids need guidance.
They aren't getting any
____________________
A few things to think about
1 - Saying something is "stupid" is the end of the world in some families, and normal conversation in others. In GOOD families, both concepts are used. If you don't allow the word stupid... You need to substitute words you do allow. Babyish, boring, uninspiring, won't work, not my cuppa... Whatever. Kids aren't parents / adults. When they don't like something, for whatever reason, they say so. Toddlers hit/grab/cry. Kids use words. What words they use are shaped by the adults preference. If you don't tell them your preference, don't be horrified that they use other words.
((I don't allow the word "boring" in my house, for example. Uninspired, on the other hand, is okay. As is "Id like to do something else / ________." Or "I can't think of what to do." / etc. I don't get mad at kids who come over and say "Im bored" or "That's boring". Instead... I say... "Hey Jimmy! No ones bored in this house. Bored doesnt have a solution! Bored is totally terminal. Worse, it means we clean! I don't wanna clean. So Im reeeeally hoping you're just wanting to do something fun, but don't know what!" / "Yeah Mrs Kiddos Mom! We want something fun to do!"))
2 - Swearing is something not allowed in MOST families... But kids do it anyway, until corrected.
$&#%!
Hey, Jimmy! We don't swear in this house!
Whoa! Your mom has really good ears! / Yes Mrs Kiddos Mom!!
3 - I don't want to hurt the mom's feelings / I feel bad saying no / my sons self esteem is getting a big hit
... Priorities.
Your own kids & family 1st
Little people 2nd (as in, you're the grown up, you make the decisions)
Adults outside the family 3rd
INSTEAD of
Neighbor lady 1st
Little people's wants over your own families needs
Your kid and family last
4- how many times can you say no?
As many times as you're asked, when the answer is no.
DONT say No, No, I don't know, Maybe, I guess, Yes.
Kids are smart. That just means they ask you 6 times
If you bought a lottery ticket, lost, but only had to ask for a million bucks 10, 50, heck... Even 5,000 times? C'mon. Anyone would say "Please" 5,000 times for a million bucks. That's EXACTLY what giving in does. It tells any smart person to keep asking.
So when you mean "No." Say "No".
5- Don't Bluff.
Parenting comes with an awesome superpower: What you say is going to happen, happens. How cool is that??? But you have to use it. When you say something is going to happen, or not, then make it happen.