The bible in parts is obsessed with sex. Thou shalt not do this,that and the other.
The family,particularly June,was indoctrinated by various chapters in the bible which speak of differing forms of sex,,to which June had adhered to,and was passing this,,her way,,,on to the rest of the family.
I often wonder at June herself not having borne children,,whether the reason was a medical one,,or whether she'd treated it as a sin. It was a dirty word in her mind and became an obsession.
Sheila was rebelling against June's wishes. Hence the abortions,miscarriage/s and finally the twins,who by this time,poor Sheila wasn't in any fit state to appreciate that she had something of her own to love and be loved by.
What a very sad ending for the poor " tortured " woman who was driven to despair.