Learn English – Now and forever

Your method of removing the others is indeed correct. At least, that is what I used to do when I was in high school.

Always try using "I" or "me" in the singular, for the same sentence. For instance, people might say: "Robert and me are going to town." Which is wrong, because one does not say "Me am going to town." Therefore the correct way to say it is "Robert and I are going to town."

However, this sentence is also wrong: "The police arrested Robert and I", because if it were in the singular, one would not say "the police arrested I", it is, "the police arrested me." Therefore one should say, "The police arrested Robert and me."

Careful (not to say pedantic) speakers place 'only' directly in front of the word or phrase it qualifies. So they would say: "I drink only water." The claim is that saying: "I only drink water" could be interpreted as meaning: "Drinking is the only thing I do with water, not washing in it or playing with it, etc."

In theory there may indeed be cases where the placement of 'only' is a source of ambiguity. In practice, however, it is unlikely that anyone would be confused, particularly in spoken language where intonation contributes to meaning.

"We have only seen a few of the sights of this marvelous city" sounds perfectly natural to me, a native speaker. In fact Google returns 3 times as many hits for "I have only seen ..." as for "I have seen only ... ".

As an aside, the sentences are in the present, not past, perfect. But the tense of the statement is irrelevant to considerations of where 'only' should be placed.