Did the structure need OC approval?
Did the structure need council approval?
Is there any record of either?
If there is a record, does it show construction details (which may answer some questions about how solid it is)?
Does the Land Titles Office have anything registered for your development (handy to know about other stuff anyway)?
Ditto for the council?
Is it shown on the strata plan as common property or part of a lot? That should be definitive about who owns what.
If there is no record of anything, I suggest that the EC engage a strata specialist lawyer to advise on who is responsible to do what where. I would suggest that you want advice that is practical to let you and your neighbour continue to have the convenient access provided by the structure while protecting the other lawyer/unit owner from possible liability and also the OC from possible liability. That advice might be to pass certain resolutions now to regularise the status quo so it can continue in a correct legal manner.
I would also want to have a structural engineer provide the advice if plans and approval cannot be found. However, it sounds like you need the engineer in any case if the railing are wobbly.
The bottom line is that the OC (IE all of you collectively) does not yet know that it is not responsible for a structure that might be dangerous. Similarly, the unit owner below does not know what he/she might be liable for.
I would be seeking to ensure that everything is correct and transparent, and above all safe, with structural advice and legal advice. I would be trying to impress on the lawyer/unit owner below that it is in his/her interest to have this sorted out from both the perspective of being the lot owner and from being a member of the owners corporation. I would be emphasizing that all benefit from clarity around the situation. No losers, only winners.