How does this work? I am a new borrower but my spouse has loans from pre-2007. Is there any way to roll that into PAYE at 10% of combined income, or will we have to make two payments at 15% and 10% of income respectively? And if that’s the case, will it count the combined income towards both (for a total of 25% of combined income overall)?

I appreciate any help.

If we have a joint return and joint AGI, and one partner qualifying for PAYE but the other qualifying for IBR, this is what should happen:
1) a monthly IBR payment is calculated based on joint AGI, the borrower qualifying for IBR will pay a pro rated portion of that amount under IBR, and
2) a monthly PAYE payment is calculated based on joint AGI, and the borrower qualifying for PAYE will pay a pro rated portion of that amount under PAYE.

A couple has a joint AGI of $50,000 and a family size of 2. 
IBR payment for $50K AGI and family size of 2 is: $251.
PAYE payment for $50K AGI and family size of 2 is:$167.
Husband owes $25,000 on his eligible federal student loans (he owes 25% of the $100,000 total marital student loan debt).
Wife owes $75,000 on her loans (she owes 75 % of the $100,000 total marital student loan debt). 
Husband qualifies for PAYE because he is a “new borrower”.  His payment would be $41.75 (25% of the total PAYE amount of $167).
Wife does not qualify for PAYE, so she is looking at IBR.  Her payment would be $188.25 (75% of the total IBR amount of $251).

And remember that married people can elect to file jointly or separately and loan payments for each partner will be calculated either:
1) based on joint AGI from joint federal tax return and total combined student loan debt, or
2) based on separate AGI from separate federal tax returns and separate student loan debt.