Apps Corrupted and I don't own my account?

I've been trying to update my apps today, on iPhone, iPad(s) and iMac, as I always do and which always works perfectly.

None of my existing apps will update on the devices, a couple new ones downloaded, but one didn't. On the iMac it says the apps (literally a dozen or more of them) are "corrupted" and/or theres a message that "this (which??) update is not available for this Apple ID either (either??) because it was bought by a different user (Who?) or the item was refunded or cancelled (um no, or I'd know about it)". I don't have multiple accounts, nor does anyone else use my computer. Weird.

I didn't want to update to iOS 9.0.2 or El Capitan until after I'd updated my apps and synced my devices, but after all these problems I thought maybe the apps wouldn't update because of my versions, so I did the El Cap update but nothing has changed in iTunes. The apps I try to update just continue to try to restart updating, then restart, then restart. It says to redownload choose Store - Check for available downloads - upon which iTunes tells me I don't have any available downloads.

I've tried, in my hand devices, using the Purchased screen rather than the Updates screen, but that doesn't help. I've tried deleting apps, restarting the phone and then reinstalling the apps....still won't install/update. The "you don't own your apps/account" box unnerved me so I even went to apple.com and changed my security and password settings. I've NEVER had problems like this with apple and now it's across all my devices, and there doesn't seem to be any help online because I've beens searching for this issue all afternoon to no avail.

I'd appreciate any help that doesn't involve reinstalling and wiping my computer/devices, or using Time Machine (which hasn't functioned correctly in, and therefore hasn't been used in, over a year). There has to be a fix/update/virus scan or something that will remedy this, it's very uncharacteristic for my apple products.