Is he in year 13 - if so he has about three months to sort this. If year 12 then longer obvs. There months is fine tho.
Agree with others - think about what kind of engineering. Read up on the courses offered at a uni (doesn't really matter which as long as they do a range) - chemical, mechanical, aerospace - they need different A levels and offer a different curriculum. Which appeals?
Then yes, consider league tables but also consider how far from home he is happy being and what sort of uni - small town, big city, campus? Some unis are especially known for a supportive environment so that may be a consideration (I am thinking, anecdotally, of Lancaster, Leicester, Aberystwyth, Bangor - not saying any of these are good or not good for engineering btw! - and there are many others).
Then you may have a shortlist or a long list - have a look at the courses they offer, what appeals, what will he get the grades for. Are there any open days this Sept/Oct he can go to?
Once he has made some choices - ideally one or two aspirational (so asking for A stars and As), two at the right level (AAA) and one back-up (maybe AAB for him or similar) then he needs to fill in the UCAS for - school will help here. Also has he done a personal statement?