Forgive me if this seems obvious, but I am willing to bet that if you called the company-that-must-not-be-named and explained the situation, they will cut you some slack – and maybe even let you off the hook entirely.
If your father (and/or his company) are clients of this big research firm, they will want to keep them as happy customers. The products you have used did not actually cost the company much additional marginal cost to produce, so they may be willing to cut a deal. I work for an information provider of a decidedly different flavor (no, not porn), and that’s what we’d probably do. We’d open with “you’re liable for all the charges” but would probably settle for splitting the difference and might even let you off the hook entirely if you were longtime and/or big time customers.
(and, to be clear, this does NOT mean I think it’s ok to steal intellectual property simply because it doesn’t have an incremental cost to produce, it just means the research company probably doesn’t have probably any major expenses of its own to cover because you downloaded a few papers)