1.Uncle Sunny who is
all heart decided to donate all his salary to the new built orphanage.

2.After everyone heard the bell rang,
all hell broke loose as everyone rushed out the class.
Passable, but really "all hell broke out" means that events get out of hand and cannot be controlled.
3.There must be other
intiatives which can solve this problem because
all roads lead to Rome.

4.When everyone is
all set,we depart to the seaside.

5.Ali's siblings are
all skin and bones as their parents cannot afford to buy some healthy food for them.

6.We envy Lily very much as she owns a television which has
all mod cons.
Just passable - sounds odd as "all Mod Cons" usually refers to the way in which a house has all the modern conveniences built in.
7.I am not going to give you any tips so that all of you are
all square in this competition.
Doesn't sound right to me - better expressed: "...tips so you are all square in the competition"
8.Willy who is
all talk and no trousers always boasts about himself,but rarely take any action to prove it.

9.Although he might look very kind-hearted,it does not mean that he has a heart of gold.As the saying goes,
'all that glisters is not gold.'
10.Harry Potter's novel series are
all the rage nowadays as most of the students own them.
With slight alteration: "...nowadays, so most of the students own them."
11.You should not only focus on your weakest subject
, English but try to put in
affort on other subjects too
. Or else you might end up with getting poor result in those subject
s due to the lack of study
. As the saying goes,
'do not put all your eggs in a basket.' 
12.Although Yii's physical appearance is totally different
from mine,she is my
alter ego as we share the same hobbies and we are intimate friend
s.

13.This competition was the only chance for him to prove his talent in sports
. Howeve
r, he injured his leg and missed it
. As the saying goes,
'always a bridesmaid, never a bride.'
If you change "only" to "last", then you are fine with this expression. It means that you have often tried to do something but never achieved it.
14.when the master of
ceromony is going to announce who the winner i
s, every participants
have ants in their pants as they are very nervous and cannot sit still.
Change "every" to "all" and you've got it.
15.I think we should just accept Betty's suggestion which we rejected last week as we really do not have other choice
. As the saying goes,
'any port in a storm.' 