Company M as the sponsoring entity will provide their registered physical address for the Doc & 5500. The trustee must be a US entity, either the other owner or a corporate trustee will likely fill that role. Owner A may well qualify as a US Citizen, but his primary residence in a foreign country fogs that status a bit.
Unless it will be a participating employer, Company K can likely be ignored as there is no controlled group with Company M, however you will want to rule out Affiliated Service Group as well; or make sure you can treat it as such so you can include it in A's compensation as well.
The 1099 contractors are likely questionable. I would have him complete IRS Form SS-8(not to be filed, but for your purposes only), or separately have him answer the questions in Part II, III, & IV. There are a few key indicators in there, one of which they already violate by publicly advertising them as "employees".