It's a three week luxury holiday that it takes two working adults three years to save up for, so presumably we're talking thousands, potentially five figures per head...doubtful that the boyfriend/daughter would be able to fund it by simply 'picking up some overtime', regardless of notice, unless they're high earners.
That just isn't true.
I've saved thousands per year whilst working minimum wage, paying all my own living costs etc. It's totally possible with frugal living.
But it does mean rarely going out, IE once every 2 months and only to cheap places, only going more often if it's something free.
It means NEVER buying food or drink while you're out and about (unless you're specifically going out for a meal or drinks as your socialising thing and even then you need to keep the cost down by not having 3 courses or getting drunk). You take something from home if you're going to be out all day. Eg a bottle of water is approx £2 from a convenience store X5 days that's £10/wk, a multi pack of bottled water is £3 for 6 from the supermarket. A store bought sandwich is £3 approx, across 5 days that's £15, a loaf of bread is £1.50, block of cheese £2 and butter £2 and it'll make you your sandwich for lunch for the whole week for a total of £5.50.
You don't drive unnecessary journeys to save fuel.
You wear warm clothes and keep the heating off except for a few hours a day on medium heat during winter, putting a hot water bottle in your bed and blankets on top of your duvet.
You don't buy expensive clothes brand new.
You don't have car finance, you save up and buy something second hand outright.
You pay insurance annually because it's cheaper than the total annual cost of paying monthly.
If you dent it, you don't repair cosmetic damage unless you're able to claim it off another driver's insurance, only structural stuff or MOT fail stuff if you're paying for it yourself or would otherwise have to claim on your own insurance (I'm talking minor damage not huge crashes obviously).
You don't spend more than a couple hundred on a phone, which you buy outright with a cheap SIM only contact and you keep the phone until it's completely trashed and non functional years later.
You don't buy anything you don't actually need.
You don't live in the best places.
You cook cheap meals from scratch, no takeaway unless it's your socialising night out.
You don't have any debt, ever, except a mortgage, or a credit card that's paid off in full at the end of the month every month.
There's lots of ways to save up, but people don't want to take them because life is less happy day to day. Fair enough, but no use complaining they can't have the fancy holiday then. Life is all about choices.