1) I have a question if you don’t mind answering.
What does it mean for angels to send blessings upon the believers? Do we know what that means?

2) Could we also say that their presence near a believer is a form of protection in of itself from the devils? Ex:
They protect from the whispers of the devils

1) In general, it means that they ask Allah to open the door of His mercy to them, increasing their bounty and warding off evil

2) Yes