Can I ask OP, how old are the older children? You say there's BP issue - are they overweight or obese?
Ultimately I can understand your frustration which is presumably why you come across as being a bit fed up with it and deciding to bin all the junk food. But that isnt the answer.
Have you had a proper, sit down chat about this with the child? Calmly, no shouting, listening to what they say / what their views are?
As for comments around being pointless to go back to GP following high BP and not knowing what the GP can do - well thats rather the point isnt it? I assume youre not a GP or a therapist specialising in food addiction so there is likely a lot they can do youre not aware of
Out of interest OP, are you slim / ever suffered with obesity etc? Because its not as simple as the child not being bothered to change, or being lazy, or undisciplined, as seems to have been suggested by comments on here.
I was one of those teens. I was obsessed with being skinny, probably eating disorder adjacent, worked my arse off to stay a size 10. Not helped by a mother with her own issues and a 'feast or famine' approach to food. Got to sixth form and all of a sudden life got busier, studying rather than going out. More study periods to go to the shop. Friends who were driving so less walking.
Went to university, it continued. Diets, on and off, years and years. Im 30, 5 foot 3 and in may last year was 19stone 10pounds. Ive lost almost 5stone now. Yes on mounjaro but a lot of work besides
Im also in addiction recovery and view it similarly to that. It didn't matter how unfit I was or how many comments I had, I had to make the decision to change, just like with the drink. I.had to get the strength to pull myself up and throw myself back into the ring for one more attempt when all the other attempts had failed. It was a mindset thing, and nothing anyone could say or do would do that for me.
Its also intuitive eating. Yes the mounjaro would have had an impact, of course it has. But feeling like I 'shouldn't' eat X or 'mustnt' have more than one of Y just made me want to put 2 fingers up to the diet plan and binge. Ive learnt to eat intuitively, I've a box full of crisps, chocolate etc in my cupboard (that people buy and I rarely get through), im for the first time in my life able to eat 1 and not have any more.
Also dont forget a lot of these foods have been designed to be addictive, to encourage overeating.
I dont know what the answer is, really. Definitely GP, possibly counselling, probably speaking to the child and seeing what they want. Using some motivational interviewing skills to get them thinking about their goals and whether current actions is moving them closer or further away from that
But one things for sure. Confiscating food will do nothing but cause an atmosphere, may actually exacerbate the problem and is likely to cause a rebellious 2 fingers up attitude towards you. It certainly wont get you the result you want.