are these sentences correct?

[njanja]

Hello,

Are these sentences correct and what is the difference between them?
If i went abroad,i would stay as long as i WANT.
If i went abroad,i would stay as long as i WANTED.

If he helped them would you say he IS a good person?
If he helped them would you say he WAS a good person?

If they knew what i THOUGHT of them they wouldn`t invite me to parties anymore.
If they knew what i THINK of them they wouldn`t invite me to parties anymore.

If he knew what his son IS DOING he would never trust him again.
If he knew what his son WAS DOING ...
If he knew what his son HAS BEEN DOING....
If he knew what his son HAD BEEN DOING...

He WAS an engineer for 20 years
He HAD BEEN an engineer for 20 years.

He decided to leave her because he HAD FOUND OUT that she was in love with his friend.
He decided to leave her because he FOUND OUT that she was in love with his friend.


THANKS.

[Tdol]

If i went abroad,i would stay as long as i WANT.
If i went abroad,i would stay as long as i WANTED.


If he helped them would you say he IS a good person?
If he helped them would you say he WAS a good person?

Here, both could work for me.

If they knew what i THOUGHT of them they wouldn`t invite me to parties anymore.
If they knew what i THINK of them they wouldn`t invite me to parties anymore.

Again, both work- the present suggests a stronger feeling for me.

If he knew what his son IS DOING he would never trust him again.
If he knew what his son WAS DOING ...
If he knew what his son HAS BEEN DOING....
If he knew what his son HAD BEEN DOING...

Again, they are possible- it depends on the time- if it's present it refers to now, the past perfect refers to the past. The past tense also refers to the present, but is following the pattern of a second conditional.

He WAS an engineer for 20 years
He HAD BEEN an engineer for 20 years.
The past perfect would have to have more context- he had been an engineer for twenty years when...

He decided to leave her because he HAD FOUND OUT that she was in love with his friend.
He decided to leave her because he FOUND OUT that she was in love with his friend.

Both are OK