It's up to the individual applicant to evidence income - the universities don't have either the time or the right to investigate without side agencies. (There's a question of data protection too - I wouldn't want my tax affairs revealed to anyone without my express permission.) It's up to the parent to clarify the situation with the university, not for them to verify it from the other end.
There was a similar question earlier about benefits - the applicant has to provide full details, the onus for doing that is theirs not the the funding organisation.