Repeatedly asking for a password

We have two Mini Mac's in our house both running the latest software update. We are not overly Tec savvy and only moved to mac 18 months ago. For some time now both macs have had a problem where it repeatedly asks for passwords to be imputed, on one it is programmes like FaceTime and on the other it is the various iCloud or email accounts. How can we stop this? Incidentally it also happens on my iPad and iPhone on occasions. Thanks you in advance.