App Security

See:

iCloud security overview https://support.apple.com/en-us/HT202303

Security and your Apple ID https://support.apple.com/en-us/HT201303

If you think your Apple ID has been compromised https://support.apple.com/en-us/HT204145 to see what to do.

Using app-specific passwords https://support.apple.com/en-us/HT204397

That's a bit hard to follow. Do you mean you're connecting a device to your Apple router via the router's WiFi password?

If so, then no. Any device, whether wired or wireless, is on your side of the router's firewall. It can only be hacked if you allow it by installing malware, or giving someone remote access.

The Wi-Fi password is akin to providing a key or a passcode to somebody else to get into your home.

Can those newly-added devices with your Wi-Fi password access services on your network? Yes.

Can that access be legitimate, or can the folks with access to those devices be nefarious? Yes; both.

That’s what you’re expressly allowing.

Can somebody that’s bad at computing cause you problems? Absolutely.

You’ll want to keep your computer software and apps and printers all current.

You’ll want to keep people and devices you don’t trust off your Wi-Fi.