help him with his homework vs help him "in" his home work

There is no nuance. I don't find 'in' a natural choice there, either.

Thank for your comment.
Do you think of any preposition that makes an implication that she did her son's homework without a big change of the sentence. I mean... while I hold the sentence structure that "She helped him with his homework.", could I make the implication that accutally his mom did his homework just by choosing another preposition instead of "with"?
I recently have been tryi

youngbutsDo you think of any preposition that makes an implication that she did her son's homework without a big change of the sentence. I mean... while I hold the sentence structure that "She helped him with his homework.", could I make the implication that accutally his mom did his homework just by choosing another preposition instead of "with"?

No, because

I see... when you decide which prepositions to stick to verbs, you naturally consider the nature of a verb first. That's why come, stand, go,get etc... these action verbs can have such many prepositions. They don't have some specific meanings, so they can change their meanings accoding to accompanying prepositions. However, some verbs with specific meanings such as help should come with certain

youngbuts when you decide which prepositions to stick to verbs, you naturally consider the nature of a verb first

Well, actually native speakers do no thinking about it at all, but that is probably how many of the collocations originated. Beware the exceptions, though!

youngbutssome verbs with specific meanings such as help should come with certain prepositions supporting the meaning.

I suppose you could say that. We native speakers often unconsciously think of verb-preposition pairs as units — not as two separate words.

help with, rely on, consist of, thank for, link to, decide on, lean against, talk about, por