To tell my MIL if she wants a son to name she can go have one and not be engrossed on what I choose to name my son.

I’m a bit of a call a spade a spade person and that’s the sort of thing I might say if pushed, but I think that even if my husband had been fully on board my sense of fairness would not have let me go with using two names that were special to my family. No matter how much we liked them
Despite agreeing 100% that it’s for the parents to choose the names they want for their baby I can understand why MIL might be feeling a bit miffed in the circumstances, All the more so as it seems that the OPs family is not hiding its delight- a baby has 2 parents and doing what the OP and her OH have done gives the impression whether it’s intentional or not that one side of the family is being recognised more than the other.

Absolutely insane that she thinks she should have been consulted.
I’m also willing to bet that she isn’t happy
about your DH taking time off to be more involved with his child. MIL strikes me as that sort.

The words used in that particular post took me aback a bit, it’s an extreme way to speak to somebody. Which is why I asked if those were the exact words used, the op might have been being a touch hyperbolic given she’s quite clearly been having a frustrated rant throughout each post.

I can see why MIL could feel a little upset about it but she shouldn't be voicing that. You may have been best saying it's yours and DHs baby and up to the 2 of you what you name your child. The saying it's "my" child and "I" will name him probably plays into her thinking it's all about the maternal side of the family.

This isn’t about a name really though is it. Your mother in law sounds a nightmare but you’re not covering yourself in glory with some of the things you’re saying Op.
Hope you sort your family dynamics, enjoy your new baby .

As long as you AND your husband are happy with babys names, then no one else needs to be involved.

I think your DH needs to tell his mum that the names were chosen primarily because you like those names, not just simply because they are names from your family.

He also needs to ask his mum to call him before coming round to check if it's okay, and to limit visits to a couple of times per week whilst you are finding your feet and enjoying time together as a family.

I dont think you are wrong to have expressed frustration when the topic came up yet again, but I do think your DH needs to stand up to his mum so you dont have to have any more discussion of it with her.

You sound deeply immature and downright unpleasant, yes she’s crossed a few boundaries but she is the baby’s grandmother and deserves some respect. And I didn’t get on with my MIL all the time but I wouldn’t ever have spoken about her like you have

Agatha is a very old fashioned name, though.

Extremely interesting, but this hasn't been usual practice for a century or more, has it? I was responding to the point that MIL might have been expecting those rules to be followed in 2026.

Why did your family care about the name, they were delighted?

No, this held across all classes in England from the 18th to 19th centuries. I’ve been studying my family tree back to the 16th century and have seen these naming patterns go across my working class and middle class ancestors. It makes genealogy very difficult:

first son - paternal grandfather
second son - maternal grandfather
third son - father
fourth son - father’s eldest brother

first daughter - maternal grandmother
second daughter - paternal grandmother
third daughter - mother
fourth daughter - mother’s eldest sister

If a baby died in infancy, it was very common for the next baby to take their name. Sometimes, there were three baby boys or girls, given the same name, because the first two had died young.

It was also common for at least one of the children to be given the mother’s maiden name as a middle name.

See:

https://englishancestors.blog/2020/04/01/english-naming-traditions/

Sometimes, it pays to have a bit of diplomacy with the PILs! Why raise the emotional temperature, when you don’t have to?

This is about more than the name thing. You simply hate her, she makes you feel uncomfortable, her very being irritates you.
she sounds like my MIL…
good for you standing up for yourself, I would personally message and say you are having a week just the three of you to establish your routine. You won’t be having visitors. You need a little time away from her! She won’t change, she will be this insufferable forever, she will lose interest though. We’re down to a half hour visit every week and that’s too much effort for her now.
good luck he’s your and DH baby, don’t let someone ruin the early days

She cried?
That manipulative tactic would give me the rage

We’re not aristocrats, far from it, but looking back over my family tree, every generation up to my grandfather (born in the 1920s) has the same first second and third name, that’s going about about 6 generations so unless they were just weirdos, I would conclude it was a common thing to do.

We were lucky in our way. We named our son my dad’s first name (he cried) and coincidentally it is also the same first name as DH late father. Winner. We had one hiccup in that we gave DS the middle name which was the first name of DH step father who had recently died. He had been DH step father for 25 years, taught him to shave and all those things. However this upset DH mum because it means our son has the same full name, first middle and last name as her ex husband (DH dad). Which she found odd. 4 years later she is now over it. She understands the reasoning.

DS has an older name which is my dad’s first name and also the first name of DH dad and grandad.

My mum was really helpful and went through my mil family tree and found instances of DS name (first and middle together) occurring in her family tree some generations back. This softened the blow a little. Could this be an idea?

Plus when we are mothers, we are fiercely protective 😁

OP, you do sound at the end of your tether. It sounds as if karma has caught up with the MiL: sending an 8-year old to boarding school? No wonder there is such a distant relationship. Is the FiL in the picture? It would of course have been his decision too (and finances)

Your baby your choice. My first two didn't have grandparents parents names. My third did because my wonderful fil had died.

My grandchildren from one son, one has my name as a middle name. One has their FILs as a middle name and one mils as a middle name.

My other son the grandchildren theyre not named for anyone.

Across many cultures, naming children after parents, grandparents, or other relatives was a long‑standing tradition. These naming patterns helped maintain family identity, honour ancestors, and create continuity across generations.

If you want to know more, Google it!

OP you sound every bit as bad as she is and immensely childish on top. I feel sorry for your DH and child.

Well, I think your mother's experience is different than the average experience given that she was ill. Under normal (not life-threatening) circumstances, most people (especially women) DO care what their children are named. It's actually more surprising and weird to me that some parents are very blasé about it and don't seem to take it seriously. Under normal circumstances, I can't imagine letting someone else entirely choose my child's name with no input from me. I don't think that's being precious.

My mum was exactly like this! Well we named both children with two middle names, one from each side (our choice and what we wanted) but my mum HATED my DD first name (Tabitha) … she tried to get my whole family to side with her that I needed to change it!!! I couldn’t believe it, after 2.5 years of miscarriages, pain, surgeries ending in a caesarean and a child that was in distressed in utero, why couldn’t my mum just be happy 🤯 … my brother actually told her to behave, it’s our choice not hers … she was still awkward and said she’d call her what she wanted and it wouldn’t be Tabitha, I told her then she wouldn’t speak to her at all ( we lived on other sides of the world) … three months later she tried to get me to change the middle name from our side of the family to something completely different, not anyone in my family … she can said she’d send me the money to change through deed poll … sometimes you can’t make up these crazy behaviours!
you go with your choices - if your DH buckles tell him the next time he squeezes a bat out of a small hole he can listen to him mum if he so pleases