There are some unhealthy videos in the computer, but I'm afraid my family will find out where they are.

Put those videos in a folder, compress them, click advanced options when compressing them, choose to set a password, set a password you know, and then decompress them. Delete the folder after compression. If you are afraid that the compressed files will be deleted, you can set the compressed files as hidden, or you can hide those videos on a USB flash drive.