How to prove residency of current residence in IL state, for US Citizenship Interview?

[vsshah]

Yesterday, I visited US Citizenship Interview for an elderly couple. My role was as an interpreter. Couple has been living in Illinois Since April 2021, with their son. Their Indian passport 'port of entry' stamp also says that, they landed in Chicago. But they have no utility bill or state id of Illinois on their name. During US Citizenship interview, they passed all the questions. But, they are asked to prove residency of IL state during last 90 days. How can we do that?

Bank Debit Card line items for spending?
Affidavit by applicant and their son?
Neighbor's affidavit about their presence in this IL house?

Please help.

Thanks.