By using FreeREG and Family Search I found the following which you may already know about. Robert Kilby was buried 25/1/1741 Langford, and Elizabeth was buried the year before 15/6/1740 Langford. Children born to a Robert and Elizabeth (assuming there was only one couple with these Christian names are as follows) ; Abraham Kilby 1729 died 1730; John Kilby baptised 1/8/1731; James Kilby baptised 9/2/1732 - possibly died 28/4/1733; but no parents mentioned for this child for the death; Sarah Kilby baptised 18/8/1734 Father just says Robert, no Mother's name; Elizabeth Kilby baptised 31/10/1736 and Abraham (2) Kilby baptised 15/7/1739 - married Arrabella Armstrong 4/12/1766, she died in 1806 buried 29/1/1806 Langford. Couldn't find any Eliza, but I guess it could have been daughter Elizabeth shortened to Eliza who was buried with her Mother, but in this case she would have been 3 years old. There are also some trees online, which will need checking out as quite often they are copied from one to another, anyway the additional info for what is worth is that Robert's wife Elizabeth surname was Rawley, and they married in 1729. It also says that Robert was baptised 21/1/1705 Cockayne Hatley, Beds.
Regards.