I wouldn't worry too much about what company it relates to - I've been in the industry 15 years now and worked for 3 different passenger companies (one of which was GWR) and a freight company and they are all broadly the same (as they all derived their terms and conditions from BR originally, with minor tweaks along the way to lead to where they are today - it's not as though each company has a completely different set of policies).
So it's a bit of a balance really - yes, you might miss birthday parties and events on evenings or select weekends, but equally you'll get full days off with the family during school holidays. That'll typically be a few days in a row, too. During which time, you'll leave work at work and broadly not have to think about work - it's certainly not really a job you take home with you (don't know what you're doing now to compare, but worth thinking about).
The whole industry (bar freight) works this way as the timetables that the trains run to come out 6 monthly. The train crew plan is then built around the timetable and runs for 6 months. The roster is fixed for that period, however some of your shifts will be "spare", which means you will have to be flexible as you can be moved +/- 3 hours (typically with the possibility of having the day extended by up to an hour) from the published roster times (eg: a 0500-1300 spare could become 0310-1155 etc).
No. Holidays are rostered on a rolling pattern (typically with 10 periods). You'll essentially move through it each year. The pattern will probably be something like:
A: W/C 1st Jan, 28th March, 1st June & 7th June, 21st Oct
B: w/c: 7th Jan, 14th April, 14th & 21st July, 28th Nov
Etc
You may start with pattern A in 2025, you'll then move to pattern B in 2026, pattern C in 2027 etc.
(Note - the dates I've put above I've just made up, dont take them as actual).
Typically from late the year prior, you can start swapping your leave weeks around. This can be by applying for vacancy weeks (eg: not every week will be full, there will be some weeks available to swap into) or you can arrange an exchange of leave with another colleague. Basically the bigger the depot, the easier this is. At one of the TOCs I worked for, we had in excess of 300 drivers at my depot and I never didn't get the leave I wanted as a result.
EDIT: Sorry, I should add that allocated weekly leave, as described above, accounts for approximately 25 days out of 34(ish). In addition to the weeks that you are allocated (and can subsequently swap), you'll have an additional 9 floating days that you can take as you please. These will always be subject to demand, however, so say you apply for the 22nd amd 23rd July, it's perfectly possible one day would be granted (there's a defined number of drivers that are automatically granted leave for a given day) and the other "subject to traffic" (they'll let you know if you've got the day off at 72 hours notice, subject to them being able to cover your shift). Essentially, subject to depot size, a certain number of drivers are automatically given the day off (at my depot it was 10 drivers per day). If you're the 12th person to apply for that day, you'll only be granted the day if they can cover your shift.
That sounds like a sensible and workable solution!
Pros of driving would be far more time off when you're not working, and potentially more time at home when you are (eg: whilst you may be working the morning and miss that hour before the kids go to school, you won't be as stressed and have a lot more time to spend with them in the evening). It sounds like shifts appeal to you, so why not apply and ask these questions at interview? If the managers don't sell the role to you, you could always withdraw your application.
Cons would be the tiredness. As others have said, you do feel jetlagged 24/7, especially on some shifts that don't work as well with your circadian rhythm (for me, it was early shifts).
I'd recommend you go for it, pose the questions at interview and see how you feel!