Goes to the sea

(a) He goes fishing in the sea at dawn.
(b) He goes to the sea to fish at dawn.
(c) He came back from the sea at dawn.

Can I say,

They go back home from sea before dawn.

They come back home from the sea before dawn.

I got confused. Do we say:

(a) He went (back) home from school.

But, why don't we say,

(b) He went back home from the sea. (why?)

He started at home, so we normally say:

(a) He came (back) home from school.

(b) He came back home from the sea

The best way I can explain it is this.

Suppose the fisherman's wife was at home when he left for sea.
She says: He came back home after a day's fishing at sea.

If I am his teacher at the school, I can say: he went back home from school.
His mother at home would say: he came back home from school.

But nobody is usually out at the sea saying: he went back home

Many thanks, I really get the clear picture!!

Sorry, I got a few questions to ask, can we say:

(a) John set sea at dawn.

(b) John went fishing in the sea during / when dawn.

(c) They line up in a queue at the bank.

(a) John set off to sea at dawn.

(b) John went fishing in the sea at dawn.

(c) They line up (in a queue) at the bank.-- a queue is a line-up; one or the other is redundant.