Yes, 'for free', is grammatically correct.
Yes, that is a grammatically correct phrase. You might use it as follows: I answer questions as well as possible.
yeah it sounds grammatically correct
yes, it is
No. The term should be "These."
The phrase "had already left" is grammatically correct. The phrase "had already been gone" is not grammatically correct.
Yes. It is a noun phrase.
The expression is "have a listen" and it is very informal without being grammatically incorrect.
Yes, the phrase 'what they're doing' is grammatically correct. For example: What they're doing is wrong.
Yes, it is grammatically correct. "Part and parcel" is a phrase that originated as a legal term in the fifteenth century. It means an essential or integral part.
The phrase 'at the discretion of' is grammatically correct. It means that a particular person has the authority to make a decision.