Wait, are your MIL and Spouse are both co-owners, and it's the primary residency for your MIL correct? Is your wife handling the money for your MIL? How much mortgage does she (MIL) pay, and you (your spouse/you) pay in %.

If she pays 100% of her own mortgage, then provides you the 10k-15k; then it's clearly a gift, and it's subjected to tax.

I think the case is this >>>> Double Check against "Gifted Money", follow the link below to the IRS website, and see if it applies to your situation.

https://www.irs.gov/businesses/small-businesses-self-employed/frequently-asked-questions-on-gift-taxes#2

Wait, are your MIL and Spouse both co-owners, and it's the primary residency for your MIL correct and not your residency? Is your wife handling the money for your MIL? How much mortgage does she (MIL) pay, and you (your spouse/you) pay in %.

If she pays 100% of her own mortgage, then provides you the 10k-15k; then it's clearly a gift, and it's subjected to tax.

I think the case is this >>>> Double Check against "Gifted Money", follow the link below to the IRS website, and see if it applies to your situation.

https://www.irs.gov/businesses/small-businesses-self-employed/frequently-asked-questions-on-gift-taxes#2