Let go of spellings --- they simply don't matter-- all searches should done in soundex.Follow the papertrail.
Death certs are imperative - they are (virtually) the only US doc that asked parents' names.And, thus the only confirming document that will tell you if you have the correct family at emigration or if there is a 2nd marriage, etc.
What about obits????They are living to ripe old ages --- contact the local libraries and ask for help.
Focus on who is your household and run down all documentation.
Here's my question -- Hugh Hasset is important -- the most important detail to date because he's in your home in 1850 --- CORRECT?He is out of birth order, so possibly a nephew.He arrived in 1850 with a Phelan, and Phelan is seeing living in WMTH (Delvin).Hugh's birth cert is available for $5.I think Phelan is a sib/cousin to John.(And quite possibly has a daughter Ellen the same age as your Ellen.)
Had you seen that 1850 census with Hugh living with them?
One guess may be that Phelan was not directly from WMTH, rather as the overseeer for Lord Westmeath (see earlier ref) lived there.But a Hugh w/that DOB was born in Delvin.