Theresa Charles was the joint pen name of Irene Maude Swatridge and Charles John Swatridge, neither no longer living, a married couple. Leslie Lance was primarily the pseudonym of Charles John Swatridge (1906-64) and taken over by his wife Irene (1904-88) when he died, though of course it is probable that she had an input in the earlier titles.
They were a very close couple and had a sheep farm in Devon.
Alan Boon (of Mills & Boon) had serious discussions with Jan Tempest about her novel Without A Honeymoon when she introduced the idea of a illegitimate child -- he felt she would encounter difficulties with the Irish audience.
As an author for Harlequin Romance, Jan Tempest published three novels. and one as Faye Chandos.
Jan Tempest's Books on Amazon: Jan Tempest
1938, Cover Art by G. Fitzgerald