"what would you say is best reddidi"
I'm not sure I can do that, but I'll give you some information which may help.
For some time most Science GCSEs (there are other options) have been organised as three groups (Biology, Chemistry, Physics) each of three modules (1, 2 and 3) plus a controlled assessment.
Everyone has to study B1, C1 and P1 (it's in the National Curriculum). If these are the only exams you do, plus one controlled assessment, you will (hopefully) get Science GCSE.
If you also do B2, C2 and P2 plus another controlled assessment you can get Additional Science GCSE. This is a totally separate qualification from Science and the grades are unrelated.
But if you are good at Science and are likely to get better grades by doing more science and fewer foreign language/humanity GSCEs you can do the B3, C3 and P3 papers and three different controlled assessments and get separate GCSEs in Biology (based on B1, B2, B3 papers and the relevant controlled assesment), Chemistry (C1 etc.) and Physics (P1 etc.).
The only thing that has now changed is that instead of getting 6 chances over the 2 years of the GCSE course (plus potentially another 3 retakes) to keep on taking and retaking exams and selecting whichever ones you did best in, you do all the exams in May of Year 11.
(I'm going to ignore Further Additional Science here as it is probably irrelevant to the OP).
So you study each of Biology, Chemistry and Physics whether you are aiming for 1, 2 or 3 science GSCEs - nothing has changed here.
And if you are on a course aiming for 3 GCSEs you have to cover and be examined in 9 modules over 2 years - nothing has changed here either.
So I don't know what anyone who throws their hands up and says "no more triple science GCSEs for our students" is talking about - what did they expect to happen, to get 3 GCSEs on the basis of the same amount of study that gets 2? And what are they going to do with the extra time if not studying for B3, C3 and P3 and the extra controlled assessment?
It seems to me that the school is either being naiive or trying to make a political point - either way they are not acting in your children's best interests.
What do I think is best? Well unless I can be persuaded that my science-focused child would get more/better grades by doing fewer science GCSEs (!) and this is worth having to do extra work to catch up with the syllabus for A level (which assumes triple science), I would be protesting very strongly to the Head of Science, Headmaster, Chair of Governors, MP and anyone else I can think of.