There are three universities that I know of in Leeds, but assuming your DS means the University of Leeds, you can take a look at these prices: https://accommodation.leeds.ac.uk/compare-residences
When I said £10k, I mean Maintenance Loan = c£5k and if parents can contribute £5k as well, that should be enough (I think OP understood me but some other PP think I meant a £10k parental contribution just to your DS).
Sadly, the fact that you have a DD in the year below (so there might be some overlap) will almost certainly not make a difference unless she goes to a London University. The reason that might make a difference is because Student Finance England (SFE) has a maximum 'assessed parental contribution' and you might go over the ceiling if you've got two at uni at the same time as long as one or both are at London universities. I'd have to look that up for you though (I'm working from memory). It would be better to plan on the basis that you may have two at uni at the same time and they both get the minimum.
Things (prospective and current) students can do to prepare:
- work and save while studying at FE level (A Levels / T Levels)
- work and save in the summer before they come
- work and save during a gap year before uni
- work during term-time* and during vacations (universities usually have info about finding local work)
- keep expenditure as low as possible (apply for accommodation early - most universities open their housing applications in about March and you'll only be invited to apply for housing when they decide which offer to accept (firm - first choice), students do not reserve accomm at their insurance (second choice) so if they end up going there, it may cost more if the cheapest rooms have gone
Term-time work will depend on course intensity (number of teaching/lab hours, etc, per week). Some universities/courses have got quite strict rules about not working.
10 hours per week at NMW is around £350pcm.
Edit: removed something that was speculative.