It's not that difficult for the sort of dates you are interested in - but you need a few certs and details to start you off on definite links to your Hastings family. Working back in time is much easier than working forward, or sideways (e.g. for siblings) - so it will probably be easier to find parents and grandfathers of Denis rather than some of his brothers and sisters.
Assuming that birth record mentioned earlier is correct, then some
possible siblings for Denis appear on the BMD Index, but details cannot be mentioned here as they are too recent for the living people rule. Look for Hastings births in Limerick district with mother's maiden name of Hughes - see :
Hastings/Hughes birthsShane
