I have balance issues (mostly when I'm tired, ill, or in the dark - when my eyes can't help me out)
I would recommend, if it hasn't already been done asking for a CT or MRI - as they are the tools typically used to determine EVAS (enlarged vestibular aqueducts syndrome) which is one of the main causes of both hearing loss and balance issues.
I'd also encourage him to walk with various "push and walk toys" (toys with wheels and a grab bar like those
shown here, that are meant to help with walking and balance - that way you can know for sure it's a balance issue and not a muscle tone or other issue (make sure the "walking bar" is one of the higher type if he's much taller than an average 12-18month old)
One thing that I find is "transitions" (sitting to standing, Laying to sitting/standing) are the most prone to exaggerate my balance issues (I also have low-ish BP so I feel "uneasy", and a bit dizzy when I get up too fast sometimes). Helping him sit up, then slowly get to a stand (and hold on to him for a min or so while his balance "stabilizes" might allow him to feel more steady on his feet.
Actually - the "positional vertigo/balance issues" made me think of something else to have the doctors test as well .... It might be worth having them check his BP (Blood pressure) while laying down, then sit him up and
immediately recheck his BP for changes (a drop in BP),then let him sit for a few moments, and recheck his BP
again (see if it's come back up, if it dropped). Then after he's been sitting a min, quickly stand him up - and re-test the BP again (looking for a sudden drop).
While children tend to be less prone to major positional blood pressure changes (because they are smaller and the distance the head travels from laying to standing is 1.5' to 2.5' versus 5' or 6' in a teen/adult) - it DOES happen, and can cause all sorts of issues regarding mobility (because every time they transition from one position such as laying to sitting, sitting to standing etc 'the wrong way' they feel like they're going to fall over, feel light headed, may even get an intense headache for a few mins etc).
If he's generally meeting other milestones (fine motor, gross motor, foods, etc) then I wouldn't worry too much at this point ... every child is unique and provided they aren't universally delayed (holding their head, muscle tone issues espeically) then it's likely just "normal variations in milestones".
A very good personal example that might put you at ease is my own niece who is currently a 11.5monthes old - she has NEVER crawled (she can't even get INOT a crawl position herself or 'hold' the position if someone puts her into a "crawl". She also 'rolled over' MONTHS late, and has been completely unable to get herself to a sitting position without help and only did this for the FIRST time last week (at 11.25 months!!). That might sound " very delayed" except that she has been
walking assisted (she'll hold our hands and RUN) for
more than 3
months now and is wearing size 2T and 3T clothes (so her body length and weight was inhibiting her crawling and sitting until her arm muscles got strong enough).
Every child is different!
One thing that I would absolutely encourage is making sure that he's surrounded with language - personally (as a person who was born Hoh , and completely deaf on my right) I'm a major supported of Bilingualism (I live in Canada, so knowing and using 2 or 3 or more languages is a very typical thing). For those of us who are Hoh/Deaf, English and Sign Language (either 'pure' American Sign Language, or CASE/PSE which uses ASL signs in a more "English order") is a natural way to not only ensure that we have full access to language, but also all the benefits (mental development, social, cultural, educational, and economic) of bilingualism/multilingualism). It's also very important to do LOTS of reading and interacting with written words, books, flashcards etc.
TaylorJade - If you'd like to chat about anything, please feel free to PM me