part time employment

Hi
has anyone else had this problem and if so what was the outcome or has anyone got any advice

we are in the process of applying for a mortgage and have been told we might have a problem, because ...

my partner has 2 permanent part time jobs both are with different members of the same family,
the 2 jobs come to over 40 hours a week , he started both jobs 4 and a half years ago

why would this effect his ability to get a mortgage

any feedback would be appreciated

Thank You
J
xxx