Surveyors will give an audit of works done but that would require access to the units and you are unlikely to get that from uncooperative owners.
My thoughts are that you start by seeking mediation at Fair Trading with a view to the owners either seeking by-laws to approve their renovations retrospectively or return all common property to its previous state.
I would also, separately, start an action on the timber floor as that is a change whose impact can be established outside of the unit concerned.
Meanwhile I’m not sure what you mean by “they’re refusing to participate in the SP, in fact stalling, unless it is of benefit to them.”
Does that mean they aren’t attending committee meetings or preventing them from taking place, or what?
Regarding the owner’s husband’s outbursts, you should consider adopting a code of conduct or standing orders (see this post ) or even employing a security guard for your next meeting