Ditto Jax's response. I would handle this with the fact that each of these folks is my customer. While there is no expectation of privacy between the applicants, per se, there is also no need to divulge more information than necessary.
If I denied them, I may say only "excessive obligations" and I would resist saying there is this $20M credit card debt outstanding.
I don't really know what either of them has in mind or what they have communicated to each other. I would handle the transaction as all others, professionally and discretely, respecting each persons confidentiality.
My opinions are not necessarily my employers.
Rules and Regs minus Relationships equals Resentment and Rebellion. John Maxwell