We need to draw a distinction between what extra OP's DS can do to secure an offer vs what they need to do to secure the grades next summer to meet their offer.
If DS's college or school has a policy of issuing predicted grades now and not changing them thereafter, then the focus needs to be on the Personal Statement. If, on the other hand, there is scope to show continuing improvement in, say, History, there might be opportunity to increase that predicted grade to Astar. This, at least, would put OP's further up the ranking of applicants by predicted grade (if that is a factor at either U of Bath or York).
In relation to securing grades next summer, then the priority is ensuring the Biology moves into 'safe' B territory (as a C would potentially harpoon both U of Bath and York). If OP's DC sat French AS this summer, then at least there is now extra study time released to focus even more on the Biology. After that, the priority is maintaining the Politics at Astar (otherwise Bath is harpooned).
A suggestion (note of caution: from someone not familiar with Pol&IR) might be to emphasise, in the Personal Statement, familiarity in and comfort with quantitative analysis (assuming that is true) as U of Bath's alternative offer appears to 'reward' Core Maths and AS Maths or Stats. U of Bath will be able to infer that from the Biology A-level but it perhaps does no harm to tease that out in the PS (without going OOT)?
Finally, there is a lot to be positive about and OP's DS needs to focus on that. As PP highlight, his GCSE profile is very good; he has been working hard on three content heavy A-levels and French AS; he is clear about the subject he is interested in and wants to study at uni; is very good at that subject; has secured relevant work experience; has predicted grades that match the typical offer of U of Bath and exceed that of U of York; and has displayed the work ethic to pull the Biology into B territory. That is a list to be proud of.