couldn't we use "those boys are nice" as a translation?
"Nice" does not mean "hezký" when used for people.
Why is beautiful not accepted?
We use the word "krásný" for "beautiful". It's stronger than handsome/pretty.
Should it be "hezčí"?
Hezčí is the comparative form of hezký.
Why "more pretty" doesn't match? For my point of view in czech we use hezci as comparative: hezci nez....
No, the comparative is "hezčí". And "hezcí" is a normal adjective in nominative plural masculine animate. Shows the importance of diacritics...
Once more - typing what is heard results as wrong, they suddenly want it in English language (what is not requestd).
That sounds extremely unlikely and warrants a screenshot or other kind of evidence.