I have one DD at local uni and one living away. Both of their own choosing, pros and cons for both choices.
Staying local obviously has huge cost savings.
But it also allows students a comfort zone to mix the unknown of uni with the safe place of home. In many cases it provides a clean and comfortable space for study and working on assignments. It also allows the students remain in existing sports teams or other local hobbies, and stay in contact with local close friends.
For some students it can be a great choice.
It is a very popular option in my university home town.
I would highly recommend part time work for all students staying at home, to build resilience and maturity and experience a different type of independence. It will also give them something to put on their CVs for when they look for college placements or internships and their first real job.
Moving away really builds independence. Shit will happen and they need to fix it on their own mostly. Getting lost, running out of money, burning dinner, forgetting to buy groceries, problems with phone credit/contracts, problems with credit cards, so many smallish things they continuously need to deal with. Not to mention no parents cramping their style on the social side of things or noticing that socialising isn’t leaving enough time for study.
For most students that works brilliantly. But it does come at a considerable financial cost.
And it doesn’t suit all students. Downsides can be homesickness. It can be very lonely, it can be difficult to make friends in large courses. The freedom of nobody watching can means socialising of laziness means classes are failed. Anxiety and depression can go unnoticed for longer, are easier to hide.
It can be harder to do part time work, as they also have to fit in laundry, grocery shopping, cooking, as well as coursework. Of course many do so without issue, but it is more juggling.
So not one size fits all, both are good in their own way.
If you were to upsize so there is room for 4 adults, your DSD and DS will need to know that the money is going into upsizing, and therefore much won’t be available to top up their loans. But if they commute to local Uni, they will have a free place to stay and that they can start their working lives in considerably less debt.
I still recommend starting a spreadsheet, to get a better understanding of the additional costs, understand the loan options, etc.