how do i find my son-in-laws photos?

You have not provided enough information. Are they on your computer or iPad? Are they attached to an email? Are they on a storage device? Are they on his computer/iPad?

Your son-in-law has to upload them to iCloud, choose to share them with you, then you will receive an invitation (with a clickable link) to view them.

Having access to someone else's images without their permission would constitute a breach of privacy and is illegal.