The words are almost identical in meaning. "Cosset" and "pamper" describe risking problems by shielding someone from discomfort, but it might be harmless. "Spoil" and "overindulge" are used when you actually cause problems, and it is harmful. If you had a hotel and wanted people to believe they will be treated well, you could say you pamper them. If you say you will spoil them, you have to say it with a smile. If you say you will cosset them, no one will know what you're talking about. It's a rarely used word. "Overindulge" creates an image of excess and discomfort; not good for your hotel ad.

Do you intend to use the spelling "Adrain"? "Adrian" is a more common spelling. On the other hand, I learned of the early American mathematician Robert Adrain because of you. Thanks!

I've never heard the word "cosset" used my entire life and I'm a native English speaker. (I just looked it up and it is a word to my surprise). All of these terms mean to be treated really well (almost too well).