Marg

Ref your question:Would RQ have given up his new baby to be brought up by two of Esther’s brothers and who is, presumably his own brother Samuel?

Samuel was not Robert's brother. But he may have been this person:

Samuel Quine d 15 Dec 1811
married 23 Feb 1773 (Braddan or Santan)
Isabella Kissack d 1825

I think Samuel was a Cooper in Douglas

Three Kissack sisters married Quines (children of John Kissack d1759 & Isabel Moor d1800.
Elizabeth Kissack married 1768 Thomas Quine
Issable Kissack (died 1825) married 1773 Samuel Quine of Douglas their son Samuel Quine married Catherine, grandson Samuel mentioned in Will of 1825
Esther Kissack (Esther d 1793-2 Bra) married 1789 Robert Quine (of Later Arderry family, one child Margaret Quine)