Older step children disciplining toddler

[Anuta77]

Hello,
This is partially a vent and I was wondering if this is also a "normal" teenage behaviour: SC who rarely see our toddler (their choice to stay at their mother's living their lives and having DP visiting them there) think that they have to discipline him.
SD (12) comes EOW (that's about 3-4 days per month), her older brother (16), every 2 months or so.
An example with the older brother: the toddler (22 months) poored cereal on the floor. I dealt with it. SS wasn't even present in the room, but once he learnt that it happened 10 min later, I see him standing in front of the toddler loudly saying "NO!". I'm sure that toddler didn't even link the 2 events. I explain to him that it's not necessary to discipline him in addition to his parents, but he just walked away.
SD is obviously with us more often so I see her repeatedly saying with a commanding voice "No!" to the toddler many times throughout the day. Obviously, if I hear it, it's because I'm present and 1) either I don't think there's anything I need to be involved with and 2) if there's something, I can deal with it. I told SD several times that me and her father can discipline our toddler when necessary, it's not her job, but she continues. Herself, she doesn't like being disciplined by the older SS who likes being bossy and ignores him.
Yesterday, we were at a friend's house and I allowed the toddler to play with billiard balls, just putting them gently from one place to another. I was sitting right next to him. She sees it, runs to him and starts saying "No!". I even tell her that it's me who allowed it (as if it's not obvious that I'm sitting 5 cm from him) and she argues with me that he can break them (hard balls and carpet flooring!).
She also tried brushing his very curly dry hair after I told her (and she argued with me) that this kind of hair should not be brushed. She did it once behind my back, but yesterday, she started in front of me.
The other time, she started contradicting me when I wanted to remove my toddler who got too close to some Rottweiler that I've never seen before. This dog's mouth was big enough to swallow my son's head. SD wanted to caress him, it's her choice, but when I explain why I don't want my son next to an unknown big dog, she just walks away. This situation with dogs happened several times, my explanations don't matter.
When she sees me changing diapers, so always asks why? Did he poop or pee? She could ask it several times per day. I don't think it's curiosity, she's been seeing me changing diapers for almost 2 years. A variation would be: did you already wash him? I just don't know how to answer this and be sincerely nice, it's just annoying.
And there are many many things like that, that make it unpleasant for both of us I suppose. My toddler doesn't go to the daycare yet, he's with me 24/7, it feels very annoying to have another child who still has a lot to learn herself to dictate to me and to her little brother what to do.
I know several women with older daughters around SD's age who had babies, but none of them tells me that they contradict or discipline them. The mother is always respected. Is it because I'm a SM that my opinion about my own son doesn't matter?

Well cough, if you leave your kids in someone elses house I think they have a right to say no if they are misbehaving.
I agree, but this is not the case. The toddler is always under my case. If I'm not there, I wouldn't even know that she's disciplining him.

Just be firm and consistent. Even if you have to tell her 20 times a day.

Its their brother and you are being precious OP. Be glad they love him like you do and try facilitate their relationship by encouraging them, not by being jealous which is what you sound like.

The more you post the more it sounds like you just cannot stand the poor girl and if it's as obvious in person, no wonder she only wants to see her dad EOW.

She saw him EOW before I came into the picture, because my DP believes that children should only have one permanent home and not travel from place to place. That's the reason why he visits them in their houses.
Like I mentioned before I loved her and even then, she would whine after 2 days with us asking when she's going to go home. Eventhough she looked like she was having fun, doing activities, playing with my older son and his friends. Way before the baby was born. She's very attached to her mother, even sleeps with her still. Nothing to do with my attitude towards her. I wish, like many SMs on this board, to have a good relationship with my partner's children.
I didn't mention in this post that after the toddler was born, my poor SD started telling me that I'm stupid, ugly (but that she couldn't call me old, because I'm younger than her parents and thus, she would be insulting her parents), etc. She also started hitting my son when nobody was watching. There were many things that happened in addition to her just disciplining my toddler. Just yesterday, she would hold his hand very strongly for a while. Yes, he tried to hit her (she's very tall and pretty strong), but I was RIGHT THERE and I ALWAYS correct him. I had to release her hand. It was basically her holding his hand and me, trying to release it. What was I supposed to do? Just watch?

Yes, I can have insecurities, I'm a human being with a difficult childhood, but it's not just up to me to suck up things that I don't like. I tried and it didn't work. I do need to create well defined limits that I feel good with. I never took anything away from SD, I served her, gave her massages, made sure she was comfortable with us, she uses my things (including an expensive piano that I bought, whereas her parents are too cheap to buy her one). I had enough of sucking up to DP's children's rudeness.

To me a big sister would play with her sibling, kiss him, hug him and call me if there's something. Not try to take over.

If she's 12, she'll rightly assume that she can deal with 99% of incidents without telling tales on the baby. Getting a parent to deal with the baby is what you'd expect a much younger child to do.

Am I right to think that you're the third wife of a Cuban man who is very friendly with his exes and these exes are very pushy and ignore your boundaries? Perhaps in their culture women all chip in and help with the babycare and dsd sees herself as one of the women?

The diaper story is weird. Doesn't your h change them?

The more you post the more sorry I feel for you in your situation OP.

Is there no way you could take time for yourself with your children EOW? Even if it’s just a couple of hours in the morning each day. It might give you the breathing space you need.

I also think you need to be firmer with your DSD. I know you’re worried about upsetting her but by being nice she’s just going to get worse.

I do also think that your partner doesn’t sound like the most supportive partner or parent and I’d be thinking about my future with someone like that.

It sounds to me like you are all missing the fact the child is desperately trying to fit into your family.

It’s entirely natural that her relationship with your son would change - he has her dad and her brother all the time and she doesn’t.

And when she annoys you she gets your attention. Which it sounds like that’s all she wants. To be a full part of your family, secure in the knowledge that she’s just as important as your son to her brother.

My DP is not a man who pays attention to little details and he's often working at the computer or doing renovations, I'm the childminder
Why are you with this lazy shit of a man?
This aggressive shit of a man who chooses to hit instead of communicate like a mature adult?

It's no wonder DSD and DS are messed up - their parents are batshit!

Op it sounds like part of her behaviour is a pattern she's had for a while.
My own ds will moan about going to his dfs because he went through a tough stage and he didn't feel like his df was there for him. Even when he was having a good time it just stayed a pattern.

To the part about her getting overly involved, she maybe a dc but she will one day be an adult and some adults are just like that. It maybe that she's just bossy and righteous.
My cousin was like this when she would come to stay, she would drive my mum up the wall, always telling my mum how to look after her brother.

Part of her is still like that now as an adult and the other part of her behaviour was because she needed to feel some control. As a 7 yr old she didn't have much, especially with how her mother acted.

Tell her to stop then.

Its not her place to discipline him, doesn't matter what anyone else says. I don't like the sound of what you've described. Don't overthink, just put an end to it, and that's it

I would get the dad to speak to her if she isnt listening to you, and maybe she will learn to respect you. I would find it extremely annoying that she is ignoring your rules that involve your toddler. Its all about learning everybodys roles in the family and different familys expect different things. You are the toddlers mother so ultimately you decide what is acceptable and your oh should support you. I dont think you dislike your sc but you could end up resentful if it continues.