In the examples you have written, you can use either "far" or "far away." Most of the time, these have the same meaning. But, I can think of one example when you must use "far away," though I cannot explain why since I'm not a grammarian. Here is what I mean:

CORRECT: My father is far away in Brazil.

NOT CORRECT: My father is far in Brazil.

There's no difference in meaning. The 'away' is optional.

This is a purely personal opinion derived from a non-native speaker, so please don't take it seriously.

By using 'Far away', it seems like you are indicating two points: 'here' and 'there'. 

Since in most situations the location 'here' is the current location of the subject, using 'Far away' tells the reader that something(or someone. the direct object) is at a distance from the subject, therefore giving the impression of awkwardness when the additional adverbs are applied.

although in any case, using 'far' doesn't sound half bad to me anyway. I guess 'far' can be used more generally.

I can't elaborate because I'm not professional enough to explain grammar in a language other than my own

I'm no teacher nor am I particularly knowledgeable when it comes to English grammar, but I would say they're interchangeable. One might roll off a native's tongue more often than the other in certain situations just because it sounds "better" or because they themselves have a personal preference, but they're essentially the same.