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AIBU?

Share your dilemmas and get honest opinions from other Mumsnetters.

How to deal with this situation? BIL & his kids as a result of an affair?

299 replies

jojobooh · 20/11/2025 14:41

Basically my BIL had an affair behind his long term partners back (has a son (10) & a daughter (14) with her) which resulted in twins being born who are now 5.

The kids have never met and are not aware of the existence of each other because of several reasons.

We have DC who are closer in age with the twins and have play dates often.
Our oldest DC talks and understands and is very cleaver.

DC see both lots of cousins, obviously separately and are aware that they are cousins and family etc.

Were having a Christmas party for all the kids in the family next month in our home, just abit of festive fun for the kids.

Now as the kids are not allowed to meet each other BIL wants us to host the party twice to neither of the kids miss out.
I think this is absurd.

Whilst we want all the kids to be treated fairly and equally I find this request unfair and OH is supporting BIL.

Why should we have two parties?

Moving forward I think this will be a similar trend when DC have birthday parties etc or other future family events we host.

And when DC are older they will be forced to keep this secret which I don't think is fair or right at all to swear young kids to secrecy.

I just wanted to see if I was BU about refusing to host this second party and if anyone else has been in a similar situation.

OP posts:
notatinydancer · 20/11/2025 15:33

Two parties is insane , so is expecting your kids never to mention the twins to their older cousins. I hope they don’t get into trouble when they inevitably slip up and how awful to be complicit in all the lies, what is that teaching them?

MinnieMountain · 20/11/2025 15:35

Does he really think his middle children don’t know? Our 12yo told us a couple of years ago that he overhears lots that we say,

jojobooh · 20/11/2025 15:36

OH did try and tell me when the twins were born.
He made a joke "BIL has quite a football team now" and I said "What do you mean?"

He said BIL had twins with another woman and by my reaction (horrified, disgusted and angry on his partner's behalf) he told me he was joking and it was a prank.

I thought nothing of it as nobody in the family mentioned anything but I did keep asking him why he said it and it came out of nowhere.

As PP points out I am worried about the kind of message it will teach my own kids.

OP posts:
vitalityvix · 20/11/2025 15:36

I started typing out a long response but essentially, this whole thing is absolutely absurd and I would say no, I’m hosting one party & no, my children will not be carrying hugely sensitive family secrets.

godmum56 · 20/11/2025 15:38

BeelzebubsMother · 20/11/2025 14:45

I think you should point out that his secret wouldn’t last past the second party!

this

TeenToTwenties · 20/11/2025 15:39

This has disaster written all over it.
The older kids will be more upset the longer it takes for the secret to come out.

TofuEater · 20/11/2025 15:40

I'm amazed the kids haven't started blackmailing him yet

Bestluck · 20/11/2025 15:40

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notatinydancer · 20/11/2025 15:40

ADogAndHisTed · 20/11/2025 14:44

Twins eh?

?

Daysgo · 20/11/2025 15:41

He'll likely destroy his relationship with all his children if he doesn't come clean as soon as possible.

SheilaFentiman · 20/11/2025 15:41

so the 10 and 14 year old think their parents split up and then dad met a woman with young twins? Or they know dad has a girl friend but not that she has kids?

and what do the twins think? Do they know BIL is their dad? Or do they think he’s mum’s boyfriend?

The 10 and 14 year old aren’t going to hate BIL any less as time goes on. He has to tell them some day. Now seems the best time, since he can’t whizz back and tell them in the past.

Hoardasurass · 20/11/2025 15:42

Your BILs 10&14 year olds will hate him, their mum and everyone else who lied to them about the twins when they eventually find out you need to stop facilitating his ongoing abuse of his children
Invite all of them to the same party and stop lieing for him

MrsBennetsPoorNervesAreBack · 20/11/2025 15:42

Honestly, I think I would refuse to let my own dc have any contact with either set of cousins until they had all been told the truth about each other.

There is no way that this "secret" can be maintained indefinitely, and I would not be putting my dc in a position where they might inadvertently let the cat out of the bag and then potentially blame themselves for it.

I would not invite either set of children to the Christmas gathering, and not have any more contact with any of them until this nonsense has been resolved.

SheilaFentiman · 20/11/2025 15:42

And BIL must know that his ex/their mum might tell the 10 and 14 year old any minute. Better if he does it.

jojobooh · 20/11/2025 15:43

Yes the twins know he is their daddy and is very involved in their lives.

The 10 and 14 year old just know that their parents split up and that their dad lives alone now in his own house.
They have no idea he has a girlfriend etc.

OP posts:
Arlanymor · 20/11/2025 15:43

Please do something about it @jojobooh - you can't be paralysed by indecision this is too important. Can you and your husband join forces to hammer the point home to BIL that (a) he is going to screw up his relationship with his middle kids the longer he leaves it and (b) you are no longer going to allow your family unit to be part of the subterfuge and that you regret ever letting it start. Think about that 14 and 10-year old being lied to by everyone they know. Think about your own kids being taught that being secretive is completely fine and that people lie to those that they say they love. Rip the bloody plaster off.

Bestluck · 20/11/2025 15:48

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DoYouReally · 20/11/2025 15:48

Why are you complicit with this nonsense?

Those poor kids, everyone knows they have siblings but them.

Daisy12Maisie · 20/11/2025 15:51

I would be fuming to have even been asked about a second party.
You do what you want in terms of your child’s party. So have the party they want.
Then your husband can tell BIL the party is x day. You are fuming about being asked to lie and have 2 parties so you won’t be doing that. He can come and bring whatever kids he wants. If your husband tries to argue I would be prepared to make a massive fuss and even kick him out if necessary (and I am a placid person). You cannot start pandering to this.
By going along with it you become complicit. Don’t do it.

All 6 of his children should be of equal importance and none of them should be a secret. His middle kids will find out at some point so he is just making it worse.

Rhaidimiddim · 20/11/2025 15:57

BIL can organise as many kiddie parties as he thinks appropriate, and he and your OH can stop putting this on you.

And all the adults can stop the pretending and start blending BIL's children. If not, there wiill be ructions when they hit their teen years.

And someone should buy BIL a vasectomy for Christmas.

whitewinefriday · 20/11/2025 15:58

Not your problem that he couldn't keep his trousers zipped up

Ponoka7 · 20/11/2025 15:58

So it's likely that the first children will find out when they are teens? That's really going to have a negative effect on their lives. Which are you going to choose? Because if they aren't introduced soon, that's how it will be. It going to damage your children's relationship with both sets of cousins and you are also keeping secrets. Why have you gone along with this? This has potential to split the family. I wouldn't say the twins Mum is the weird one.

Sleeposaurus · 20/11/2025 15:58

Is it just your children and his at the party or are there others?

I have an image of the first cousins leaving and you having to explain to all the children that you are going to do it all over again the exact same, please don't mention it to the other cousins. The logistics will be epic.

Surely they are more likely to hate him for hiding their siblings from them.

Sasha07 · 20/11/2025 15:59

So... Your kids are expected to pretend the second party is their first party and go through it all twice without ever mentioning the first one or accidentally not mentioning the other kids names?! That's a big ask! When I used to do Halloween parties, kids would bring up how last year, remember how such and such ate too many doughnuts or when such and such won the game by cheating etc... the first party will be fresh in their minds and no, it's just too much to involve your dc in his twisted charade.

Wtf is going on with his family to keep the twins a dirty little secret. That's so disrespectful to them, to all of them! What an utter selfish, cowardly man. Those poor kids. Let's see how many of them will bother with him when it all comes out, which it inevitably will.

ReyRey12 · 20/11/2025 16:00

Honestly, I wouldn't entertain this. I would just have onw Christmas party. If your husband wants to organise a second one at your house, I would attend but husband can organise it. Same with parties. If brother is inviting you twice to a birthday party at his, I might attend twice if I had nothing else on. However, I would organise only one bday party for my children and brother gets to decide who to bring.

The only reason I am entertaining this to this extend is that ex SIL seems to agree with the set up. I also hope that you will realise that 10 and 14yo will absolutely hate all of you.