Hi Sez,
The information you are seeking is almost certainly no longer available. If the business was a limited company, then ownership would be determined by the number of shares and the only likely records of these would have been in the annual returns, which have long since been destroyed by Companies House.
If a partnership, then this would have been governed by the Partnership Act 1890. In either case, accounts would have had to be audited, so an external firm of accountants would have been involved. (Sole traders were exempt from this provision, though many may have opted to use an accountant or employ a bookkeeper).
Your big problem is finding out which firm of accountants were employed to do the auditing. If you could establish that then there is a very slim chance (and I mean slim) that some papers might be filed away in a cellar somewhere. Lawyers frequently deposit old papers in Birmingham Archives, e.g. the Crowder papers, I'm not so sure about accountants doing the same!
As to ownership of the building, the Rate Books, if they have survived beyond 1913 (the last year I have spotted in Birmingham Archives), should state the name of the owner and/or leaseholder. Perhaps someone who visits Birmingham Archives on a more regular basis can tell us the last year for those old bound Rate Books.
What were the exact titles of the businesses? If limited companies, there must have been liquidation notices published - London Gazette again, local press - were the liquidators the same firm that were previously the companies' auditors? Do they still exist, were they taken over, etc. ?????
I think that you've done very well to establish the facts that you have so far. You're now really in the lap of the gods!
Maurice