I apologize for this much belated reply. I had been so preoccupied with very urgent business that I overlooked checking out the postings in this particular discussion board.
From how you relate your conversation with that band leader, you did ask the right question, “Are all the members
only sons?”, and he did answer you correctly if indeed he said something to this effect, “I’m the
only son in our group; the other three has siblings.” The problem is that you predicated your question on the presumption that by naming their band “Sons of ______,” they meant to indicate that they are “only sons”—in Tagalog
“mga kaisang-isang anak na lalaki sa pamilya”—when, from all indications, they meant that they were all sons of whatever name or word it was to complete the phrase “Sons of ____,” like, say, “Sons of OFWs” or “Sons of Great Sailors.” This is why I’m almost sure that the band leader didn’t misunderstand you; he understood you perfectly and gave you a perfectly clear and unambiguous answer. It was the frame of mind you brought to the exchange that was logically faulty, and that having been the case, you wouldn’t have appreciated the correctness of the band leader’s answer even if you had asked the alternative question that you suggested, “Are all the members
sons only?,” which, by the way, is syntactically flawed and even more confusing.
Neither you nor the band leader is at fault in that faux pas, though. Both of you are just victims of the treacherousness of the word “only” as
the ultimate floating quantifier, capable of creating so much ambiguity and semantic mischief if we are not careful in using or positioning it in our statements. Our only defense against this ambiguity and semantic mischief is what linguists call
disambiguating qualifiers, or additional statements designed to clarify our meaning and eliminate ambiguity. Better still, we could prevent ambiguity from developing or getting out of hand by avoiding it at the very point of creation, so to speak. In the situation that you related, for instance, no ambiguity would have started had the band members adopted the name “Only Sons Band,” if indeed they were so as you assumed, rather than, say, “Sons of OFWs” or “Sons of Great Sailors,” which are names that leave lots of room for ambiguity of the kind that prompted you to ask “Are all the members
only sons?”—a question that, of course, further exacerbates that ambiguity.
At any rate, you’re right that there’s a chapter in my book
Give Your English the Winning Edge that gives prescriptions for avoiding trouble in the usage of “only.” I posted that chapter here in the Forum five years ago under the heading
“How to avoid semantic bedlam in the usage of the word ‘only.’” You can check it out by simply clicking the indicated link. I’m sure that by following its prescriptions and avoiding its caveats, you’ll be able to navigate well when using “only” in both your written and spoken English.