Double science ceased to be a few years ago.
Nowadays, they do "Science" in Year 10, and "Additional Science" in Year 11.
Depending on how the school organises their classes, they can also do 'Extension Units' spread over Year 10 and Year 11. If they do the extension units, they can be awarded Physics, Chemistry and Biology GCSEs, instead of Science and Additional Science.
I teach Edexcel 360 Science and here is how it works (I think it is similar for AQA). For both Science and Additional Science, the course is split into 10 modules of 10% each. There are separate examinations in Biology, Chemistry and Physics, where they do 2 modules each. In addition, they do a teacher marked assessment in Biology, Chemistry and Physics, and finally, a teacher assessement of their practical skills.
If they do extension units, there are two further units in each strand.
Whether to do Sci/Add Sci, or Bio/Chem/Phys depends on a lot of factors. Do they want to take Science A-levels? Although it is possible from Add Sci, it is easier from separate and they are much readier for January AS modules.
What about the other subjects they want to do? Do they want to do 2 MFLs, three humanities, arts, technology etc. These all need to be factored in. It can work both way for clever kids - they tend to be clever across the board. The less clever ones may have trouble filling their timetable if they, say, drop MFLs - they can still access the Sciences.
Triple Science is a lot of Science lessons in a week. They need to be broad and balanced at this stage in their education.
What are they likely to get? It is much better to get two A* than 3 As in the Sciences (and ditto for lower grades).
Does the school have all the clever kids doing Triple? If so, then it might be a good idea to follow them to avoid disruptive pupils or a focus on foundation level work.
On balance, I would say yes, if wanting to continue to A-level, and yes, if it means avoiding disruptive kids. Anything else, I would say tread carefully.