To think it can be hard to explain how many siblings I have?

I am honestly not even following and it’s written down.
Just say 4. It’s enough to highlight there’s a lot of you, but not so many it’ll get probing questions. Reality is, nobody cares enough to know the details. Sorry if that sounds harsh.

I'm jealous.
I'm an only one and it feels quite lonely sometimes.
Also, it would be nice for my DC to have aunts, uncles, cousins etc.

I have historically always told people I'm an only child because telling strangers my only biological sibling died when I was a child and I have a posthumous stepsister (of sorts) seems a bit extra for polite and disinterested chit-chat.

Since my mother's death, I struggle a little more in this regard when someone asks about family and I say "my mum is dead". If they then ask about siblings, it feels strange to admit the one but deny the other. On the other hand, I'm loathe to make myself sound like Little Orphan Annie.

I don't see why it would be a pressing question.

I don't think it need be a big deal. Most people who ask that are probably just trying to be polite and make mundane convo. Not open up a huge can of worms.

There's no right or wrong in family relationships.

If I didn't want to go into detail and was asked I'd just say It's quite complicated. Or just say 'a few' and change the subject.

I doubt anyone would press you and be desperate to know. It's very common to have half and step siblings. Or some people have close family or friends they call siblings/aunties/uncles etc.

It's how you feel comfortable describing your family that matters. Nobody has the right to judge.

I have multiple half and step siblings.

If people ask I only give the number of siblings I share a mother and father with.

Yeah not sure how you explain because my family dynamics are confusing too. Not quite as confusing but:
Only child of my mum and Dad.
1/ 4 children that my mum had who grew up in her house.
My step dad had 8 children.

We were brought up as siblings, when in contact with one another however the ones related to my step dad were also my cousins as my step dad was my Dad's brother.

If it's just small talk and you don't want to say 'It's complicated' then I'd say 'I'm the only child my mum and dad had together, but I grew up living with aunts and uncles who were actually similar ages to me, so that was like having lots of siblings really.'

I wouldn't bother to go into step-siblings and half-siblings given that that you didn't live with them or even find out about them.

It's really up to you though. If it's someone you want to get to know well - like a date or something - then say 'Brace yourself, because this is complicated' and tell them the full story if you want. But if it's a colleague or someone you're just making small talk with, you can say whatever you want, it really doesn't matter if you give them the full picture or not. They're only asking to make conversation.

This

“I’m an only child but lived with my extended family growing up and there were 12 of us kids in the house”

You are an only child if you didn’t know your half siblings, or one of 3 if you did.

and then you say you’ve also got some step-siblings.

you do not reference your mum’s 10 siblings as yours, you are not one of 12, she is 1 of 11. You’d hear my eyes rolling if you told me that you were one of 12

Go with youngest of 12 since that feels most real.

"Quite a few half siblings and step siblings"

I either state one or if I’m really going into it. Around 23 maybe more at this point as the breeder keeps breeding and sadly his penis hasn’t fallen off yet.

Only one is the only I’m in contact with and grew up with.

I’m one of many

I have 2 half siblings via my father but i have never met them so am in effect an only child

Just chiming in to say it‘s ok to misname relationships to make them fit with your experience, particularly in small talk. We have 2 young relatives in the family who are technically 1st cousins once removed. We have a close relationship with both and refer to them as niece and nephew. I think the girl refers to our son as her nephew, while her brother talks about his cousin‘s child. It‘s shorthand to understand the closeness of the relationship, which second cousin wouldn’t convey.

A school friend was close to the daughter of her much older brother.There was a year between them, so they referred to each other as cousins.

Your story could be that you grew up as the youngest of a large family. You were close to the next in age.

"I was brought up at my grandparents house with lots of aunts and uncles close to me in age" would be a less enigmatic version of 'it's complicated' but without too much personal detail maybe.
To be honest asking a straight 'how many siblings' is complicated for a lot of people these days - do you count full, half, step? What about those you didn't grow up with? I'd avoid it as a simplistic opening question.

I'd probably just say whatever feels most comfortable and change the subject/immediately ask about their family. Most people are not likely to quiz you for specifics.

I think you need to change your answer depending on the environment.

An interview? 2 singling but I haven’t been raised with them is plenty.
Small talk? It’s complicated lol. I have an arrangement of siblings, step and half siblings.
Anyone who is close enough to know your family history? 12 because thats who you really consider your siblings (regardless of whether you’re close or not. They are the people that you grew up with)

I don’t find this is asked very often, but in your shoes I’d say 2 and leave it at that unless more detail is required.

I would just say you're an only child with an assortment of step and half siblings, some close, some distant.

Or say this line from You've Got Mail

memes.getyarn.io/yarn-clip/882e4ff3-4cd3-4ff0-ac61-ca967be162ae

I once knew someone who used to talk about his sister, who was very close in age to him but was actually his aunt. His mother and his grandmother both had kids within a matter of days of each other and they were raised together. I think he generally referred to her as his sister because that’s how he saw her, but if he got more personally involved in conversations he would explain.

It’s not necessary to go into all the detail or to be mysterious with things like “it’s complicated”. I have half siblings but I just call them my siblings because that’s how I see them. In fact one of them isn’t actually my dad’s but she calls my dad “dad” and I call her my oldest sister. I think the way you feel is more important than the biological accuracy. You weren’t raised an only child, and you weren’t raised the oldest of three - you were raised the youngest of 12.

You have three siblings…..no need to explain anyone else in your life, not that they’re any more or less important.