How does uni accom work? My mums on benefits+she says she cant afford a 2 bed whenigo

Most uni accommodation contracts are for the duration of the academic year only (usually about 40 weeks or so?) rather than the calendar year. It is possible to sometimes secure a halls contract for the calendar year although these may be preferentially offered to or restricted to mature students, care experienced or estranged students, students with children/families coming with them etc. There might be options available for students from a low income background however as well.
Note though you usually only live in halls in first year (if at all) and thereafter typically live in private rented accommodation (except for Oxbridge where it's more common to live in college for the whole degree) which will more likely offer a 12 month contract. This may give you more options although it's likely you'd need to find a job to help support yourself between terms as the maintenance loan is probably not enough to cover a 12 month contract alone unless you're in a very cheap city.
Students often do go home during the holiday periods, particularly school leavers - that said at most unis (again Oxbridge is an exception I hear) your contract will cover the winter and spring holiday periods and so you would usually only need to move out for the summer holiday. Going home on weekends is less typical (I did this a lot when I first moved out to uni going to a local uni and it...did not help things overall).
There is also the option of living at home during the degree, although bear in mind if you do this while you still get a maintenance loan, it'll be a slightly reduced maintenance loan.

Have a chat with your university support team. They may be able to provide advice or support as they do for estranged students or care leavers who also wouldn’t have a family home to go to in the vacations.