Qualification for one stable income + one phd student with high grant income

My partner's stable income: 75k pre-tax

My income as a phd student combining stipend + award based grants: 75k tax free.

Credit scores: both 800+

Down payment: 20 percent

We're looking to buy something for 500k and put 100k down so 400k mortgage.

I know this is a bit of a weird situation and that banks don't look kindly on grant/stipend based income even if I did make the equivalent of a 110k salary this year since my income is tax free.

My question is, will this income count for anything at all? or they'll basically count me as having 0 income because it comes from grants/stipend which are not stable?

I have a cosign from someone who makes 80k after tax (retired, no debts) but I would prefer not use it.

Thanks for any information.