Hi, OP -
It is great that your twins have such high PGs and excellent offers.
I realise such intelligent young men are almost certain to have thought of this for themselves, but I have seen enough disasters even at this level to ask you to check with them that their Insurance choices actually have lower offers than the choices they firm.
Eg concerning the DS you wrote about, because (the remaining part of) his Warwick offer and his Edinburgh offer are the same, if he makes one of these very competitive programmes his Insurance choice and misses his offer, he is likely to be shut out of both. (I think chances that would happen given his PGs are minimal, but this does not affect the principle.) Mitigating circumstances aside, of course.
Ironically it is these top students who are rightly confident in their abilities who sometimes have difficulty appreciating this point.
Your twins can find data, I think in the Complete University Guide, on the results attained by matriculating students and which Maths programmes went into Clearing recently. Note that the attainments must be benchmarked against the offers in place at the time.
Again, best wishes to the twins