I'll only respond to the wrong ones or the ones I have something to say about. Everything else is perfect to my knowledge
(b5) It is reported him to retire soon.
(b6) It is reported him to be retiring soon.
.
(a) Some flowers were sent to he by Ben.
Nope. That should be "him", not "he".
(b) This beautiful necklace was brought for me by my aunt.
I'm not sure. I would use "brought to me", not "brought for me", and the latter is easy to misread as "bought for me". But I don't know, it might just be an uncommon choice of words.
It is said that it will be warm this winter.
That's fine, but note that "it is said" is an expression that more often refers to legends rather than simple rumors.
(a1) They didn't let me alone.
Yes, but only in some dialects. I know it's normal in British English and incorrect in American English. I don't know about any other dialect.
(a5) I wasn't let to be alone.
Nope, not that one.
(b5) It is reported him to retire soon.
(b6) It is reported him to be retiring soon.
Nope. Not even close, I'm afraid.
Would all the sentences have almost the same meaning?
(c1) It is difficult to realize your dream.
(c2) It is difficult to realize a dream
(c3) It is difficult to realize dreams.
(c4) It is difficult to realize your dreams.
Yep. C2 is a little unusual, but fine.
What's the difference between (a) and (b)?
(a) I'm glad to meet you.
(b) I'm glad to see you.
"Meet" is typically only used for the first time you meet them, and something else is typically used after that. "See" is typically only used for people you have already met before and are meeting again. It's not a hard rule, though.
"I'm glad to see you" can also be an expression of relief, e.g. if the person you're talking to is going to get you out of some predicament. This is typically the only case where you would say "I'm glad to see you" to someone you are unacquainted with.
By the way, "Pleased to meet you" and "Nice to meet you" are both far more common than "I'm glad to meet you".
Do you also say (c) and (d) meaning (a) or (b)?
(c) I'm happy to meet you.
(d) I'm happy to see you.
C is the same as A and D is the same as B. My comments on those also apply here.
Would either sentence be used interchangeably?
(a) His eyes were full of tears.
(b) His eyes were filled with tears.
Yes.
Which preposition would be used in the blank?
If I've guessed where the blanks are supposed to be:
(a) Her father was shocked
by her final decision.
(b) The mountain is covered
in snow.
(c) He was surprised
by the news.
(d) He was excited
about/for the result of the game.
(e1) They were satisfied
with the result of the game.
(e2) They were happy
with/about the result of the game.
(e3) They were content
with the result of the game.