Are these Finmar chairs Aalto?  

Hi, I dont know of you still have them but I don't believe they are by Aalto. As this section from the Journal of Design history writes Finmar didnt only import Aalto designs - it could be that yours are later war time or post-war chairs imported and retailed through Finmar:
"Finmar Ltd., a wholesale firm, was one of the major importers of Scandinavian furniture to the UK in the period 1934-65. This article looks at the operation of the company after the Second World War, from 1949 to 1952, charting the goods that were imported, consumption patterns, and the restrictions the firm faced, in order to show how the UK market for Scandinavian furniture developed. Although Finmar had imported Alvar Aalto's plywood furniture from Finland before the war, its source of goods changed to Denmark in 1949 when the company was sold to a Dane, Paul Stemann. Under his direction the company expanded rapidly, starting with Danish factory-made versions of Windsor chairs that fitted the Utility regulations, and was, by the time the Utility regulations were dropped, selling a much greater range of goods to a number of large, London-based department stores such as Heal's and Liberty's".
https://www.jstor.org/stable/1315947?seq=1#page_scan_tab_contents