On the assumption that you’re in NSW, Sect 65A of the NSW Strata Schemes Management Act prescribes that Lot Owners may not add to, alter, or erect (attach) any new structure to any part of the Common Property without first seeking and obtaining the formal consent of the Owners Corporation, which in the absence of a relevant Special By-Law may only be given by ≥75% of those Owners present both personally and by proxy at a General Meeting.
That may all sound like its a little over-the-top in the context of the scale of work that’s been undertaken at your Plan, and particularly so with the door, but just a couple implications with respect to the ceiling fan are that its presence may compromise fire safety by effectively venting the void above the ceiling, may create moisture-related problems in that area, and further, should the current owners sell the property, subsequent Owners could validly require the Owners Corporation (O/C) to maintain, repair, and replace the ceiling fan as it’s attached and extends into the Common Property (ceiling).
As the O/C is aware of the Owner’s renovations and of at least the two (2) breaches of the SCMA that you’ve mentioned in your post, it needs to formally advise the offending Owners that they’re currently in breach of Sect. 65A, and that to overcome that the O/C is willing to accept and consider an application by them to retrospectively seek its consent to all their renovations, including to the works of tradespeople whose details should be provided.
In that way, your O/C should encourage the offending Owners to make it aware of the full extent of their renovations, and may then meet to retrospectively consent to those in full or in part, including to conditions that make current and future Owners responsible for the maintenance, repairs, and replacement of items such as the ceiling fan, or deny consent and require the offending Owners to at their cost restore the Common Property to its original state.
The important thing is for your O/C to get on with it, as it’s difficult to later defend a position of awareness with no action, and also because matters of this type tend to proliferate when Owners see no repercussions arising from the similar actions of others.