It was actually never said on the show. Maxwell's wife (Sara) died many years before the series started.
Maxwell Fry died in 1987.
Maxwell Maltz died in 1975.
Jenny Maxwell died on 1981-06-10.
Steamer Maxwell died on 1975-09-11.
Maxwell Munden died in 1973, in London, England, UK.
Actually, it was never said on the show.
Maxwell Maxwell-Gumbleton died in 1952.
James Clerk Maxwell died in die
Bochum.
Cecil Maxwell died in 1973.
Lewis Maxwell died in 1862.
Thomas Maxwell died in 1864.
Maxwell Dane died in 2004.
Maxwell Bury died in 1912.
Hugh Maxwell died in 1873.
Brian Maxwell died in 2004.
Stephen Maxwell died in 2012.