Quick background: I live in a house with my sibling and their parents. My sibling is not legally or biologically related to me, but they ARE my sibling. My sibling's parents are not my parents, but we are collectively a 'family,' in many senses of the word. I call my sibling's parents "the Elders of Plumley" as Plumley is the name of our house, they are the oldest members of our household, and they are sources of great wisdom. I myself am in my late teens (no longer in high school.) My sibling is in their mid teens (still in high school.) All of us in the household are various hues of neurodivergent. (I have ADHD and my autistic friends are all convinced that I'm also autistic; my sibling is a fellow ADHDer and may or may not be autistic; Elders are ADHD and ??? (cluster of traits that are definitely something but remain undiagnosed) respectively.
Main thing: So, I have this communication issue with my younger sibling. (They're in their mid teens, I'm a few years older than them.) Sometimes I'll be trying to tell them something, or ask a question, and they won't respond; if I say their name a few times, they get frustrated with me (or, they make a noise that sounds frustrated, I'll admit that I don't know exactly what all their noises mean.) This isn't as much of a problem for me as it is for their parents. The elders of plumley have trouble communicating with them, and it has been known to cause arguments/distress. My sibling responds to them in ways that are harder to decipher, and they tend to make more irritated noises. (Or maybe they just get interpreted as irritation more often. I'm not sure.)
My sibling has previously described processing/registering that someone is talking to them, but not feeling the need to respond. I've asked about how we could maybe work out a means of more regularly communicating the fact that they're listening and similar, but they kinda just shrugged at me and made a confused noise. And to be honest, I feel quite similarly about the whole thing too! So, I turn to you lovely internet folks. Do you have any strategies for this kind of thing? Are there things I should be doing on my end to make communication easier? Are there alternate ways of saying "I'm listening" that aren't just saying the words?
I'm coming at this from a lens of hypervigilance and mirror/model behaviors, so I hope this is helpful and am apologetic if it isn't.
There's a certain range of engagement between parties in a conversation that feels "right" to many people. Sometimes that engagement from the listener comes in the form of eye contact, facial expressions, or body positions - or in the slight changes in each of those signalling devices. Most people are more highly attuned to noticing one of these than the others, separate from how well they perceive or interpret these signals overall. There could be a number of ways for your sibling to signal that they're listening - occasionally nodding their head, making eye contact at times, allowing how they're feeling to show on their face, or just small comments like 'yes', 'no', 'okay', or 'uh-huh'.
For me, learning how to perform these smaller tasks as a listener made these kinds of interactions easier overall - I could spend a small fraction of my bandwidth getting the information I needed without having to spend the energy on an argument, especially one about whether I was listening. If your sibling gets frustrated when they are questioned about listening, framing it as a way to prevent their own frustration may be a way forward.
I wish you the best of luck