Agree with others - it would be very unusual for a student who had prepped for combined science (which is triology btw - confusingly named I agree) to be put in for triple science - ie three separate GCSEs - at this stage. Especially this year.
OP there is nothing wrong with taking combined science, and it is perfectly possible to take science A levels with it.
Science has a higher and foundation tier too, so there are four options overall - combined F, (two science GCSEs with grades capped at 5); combined H (two GCSEs with grades up to 9); in both these cases the grades must be within one of each other or identical (so 4-5, 3-4, 5-5, 7-7, 8-9 etc).
Then there is triple of single science GCSEs, where a student gains a GCSE in each of biology, chemistry and physics. They can take any or all of these at F or H level, with the F grade again capped at a 5. The H paper is in all cases for more able students as the intention is that the lowest possible grade is a 4 (though in fact in recent years for various reasons it has been possible to gain a 3 in H, rather than getting no grade at all).
Does that make sense? What is your DS supposed to be sitting in the summer?