Hello. I will be grateful for some language help.

Question

1) Is the preposition "in" OK in the following sentence (maybe, no preposition at all or "when"?): "He made no mistake in choosing true friends"?
2) Is the word "contain" natural in the context: "I fully agree with the ideas the book contains"?
3) By the way, is it possibe to use "share" in the same context: "I share all the ideas the book contains"?
4) I'm not sure whether I used "one's" correctly in the following sentence: "It's a credo one should follow throughout one's life". (I feel that "you" and "your" are better but I have too many "you" for the passage. Is it possible to say just "throughout life"?)
Thank you for your time ans help.

Answer 1

1. "when" would be best in this sentence, but "in" is OK. Omitting the preposition is OK, too.

2. Yes.

3. With whom are you sharing the ideas?

4. You've used "one's" correctly, but another alternative for "you" is "a person" or "someone." Using "throughout life" works well, too.