There are so many twists and turns in this, and supposition comes to the fore.
Leander is an unusual name, but a Leander Hearne married in Fulham in 1895. That would be when Sandra's Leander was about 16.
Unity appears as Unity Green on the 1901 census, and on her birth cert dated 1897, but neither of the possible spouses in 1895 were called Green (Albert Wolfe or John Hearne [cousin?]).
If Leander did not marry someone by the name of Green, perhaps she and her husband separated and following this she produced a child whose father was surnamed Green, mother's name Hearne. (The answer to that should be found in Unity's birth cert). For while after that she could have then called herself Leander Green for Unity's sake.
Furthermore, if that 1895 marriage was Leander, perhaps she never married Alfred until 1931 because her first husband was still alive?
Supposition as I said. Unfortunately Sandra you have to embark on a rolling programme buying a few certs to find if there is any truth in any of it. Roy G