Following lines forward (from information on FreeBMD up to 1983)
https://www.freebmd.org.uk/:
William LOWTH born 1920, killed in action 1 May 1943
possible marriage Sep qtr 1939 Leicester vol 7a p857 to HUNTER, but no children found for this marriage
No other marriage found for William or William R
Presumed no descendants
Peter J LOWTHborn Dec qtr 1928 Blandford vol 5a p303
died Jun qtr 1963 Westminster vol 5c p352 age 34
possible marriage Dec qtr 1951 Ilford vol 5a p656 to SHEA
possible LOWTH/SHEA (2 sons):
Mar qtr 1953 Weymouth vol 6a p781a
Jun qtr 1958 Sidcup vol 5b p118
Kevin John LOWTHborn Mar qtr 1932 Blandford (10 Jan 1932)
Died Dec qtr 1994 Weymouth 4331B/B7D/128
probable marriage Jun qtr 1959 Sturminster (Dorset) to DOWNTON
LOWTH/DOWNTON (3 sons, 1 daughter):
Dec qtr 1959 Wincanton vol 7c p354
Sep qtr 1961 Wincanton vol 7c p432
Dec qtr 1962 Wincanton vol 7c p409 (possibly married Sep qtr 1983 Poole vol 23 p587 to TURNBULL)
Sep qtr 1968 Wincanton vol 7c p708
(half-sister) WALSHEborn Jun qtr 1938 Uxbridge vol 3a p249
married Dec qtr 1959 Poole vol 7c p1455 to EXTANCE
EXTANCE/WALSHE (3 daughters):
Dec qtr 1960 Wincanton vol 7c p420
Dec qtr 1962 Wincanton vol 7c p413
Mar qtr 1968 Wincanton vol 7c p732
Given the rarity of the surname EXTANCE, I would be inclined to have a look on FreeBMD to get the full names, then consider a site like Facebook to see if there are any on there.
Alternatively
http://www.thedorsetpage.com/genealogy/names/names_e.htm#Extance has a contact name - click on it to send an e-mail.
Good hunting.
Philip