You need to know the exact costs.
Then work out your budgets.
Perhaps you split what was going to ds, so you pay the top up for both accomm fees and they have to find their other living expenses. Teach them how to budget. Start buying some extra long life food bits on the shopping now, so you can send them off with decent food parcels. Work out how long a term is, usually 12 weeks ish, and send them off with 24 bags of pasta, 24 cans of baked beans, 24 pasta sauces. That's easily 2 meals per week sorted. Then, in semester one, do the same for semester 2.
It should get cheaper at home without them there too, adding in some savings from your usual outgoings.
Start putting 100 quid a month away now, so that come September there will be a pot with 300 each in to send them off with. Combined with a decent food parcel, this could just about see them fed for the whole term. And repeat ready for semester 2.
There are ways, you just have to do it, be disciplined and get them to understand that they will have to find some money to live off. Whether they get a summer job and save every penny, a term time job, or whatever they can.
It'll be a hard couple of years, for them and you, but it's not impossible. And they'll have a better understanding of money if they're having to source some of it themselves!