Calendar invites not being send AND Calendar invites being send to email

I have two question for two different devices.

First one:

This is an issue with an iPhone 13 with iOS 26, but this happened before the software update was downloaded.

The thing is that, whenever an event is created and an invitation is sent, the receiver doesn't get anything at all, no invitation no notification; tried sending to any type of device (another Apple, Android, etc.) and yet the other person didn't get a thing.

The phone DOES receive invites; it just can't send them. No one receives them.

Furthermore, there are two calendar accounts in the phone; iCloud (the main one) and Gmail; the invitations are sent from iCloud; the Gmail calendar is to have the Google Calendar events (sent from the device talked in in the second paragraph) in the Apple Calendar.

Second one:

This is an issue with a iPhone 15 Pro with also iOS 26, but this also happened before the software update was downloaded. The issue here is that when sending a calendar invitation instead of the other person not receiving anything at all, the receiver get 15 or more invitations to the same event; and the event is not even modified, it's just and invitation and suddenly the other person starts getting emails (because they're emails, not calendar notifications; as, for some strange reason, they're sent from G.Calendar, even though G.Calendar is not downloaded). That is another issue with this; why are the invitations being sent as emails from G.Calendar?

The phone has two accounts in the phone too; iCloud and Gmail (the one being used is the Gmail account as the iCloud one we are clueless as to where it comes from), it could be the reason as to why the invitations are being sent from G.Calendar (the main calendar is set to be the one from Gmail too), but we don't understand how since the phone doesn't have G.Calendar.

The send and receive are toggled as receiving notification.

Both devices are in the same family, but I don't think that has to do much with anything.