Should friends and relatives, to whom pornographic films were sent in their youth, be informed that they watched them? And does the ruling differ if they are relatives or friends? And does paying for their food become unlawful until they are informed, keeping in mind that informing them might cause a problem?

If you are doubtful whether a sin occurred before or after puberty, the default assumption is that it was before. Repentance to Allah is among the best of deeds, so repent to Him and seek His forgiveness. You are not required to inform them that you sent them these things. Rather, strive to remind them of Allah and the impermissibility of watching what displeases Him. Replace sending what displeases Allah with sending beneficial clips that please Him. And there is no sin upon you in eating from their food without informing them.