Would be good to see what the 1863 marriage cert stated regarding John and Margaret's parents to see what links can be made back to their families.
Jonn has found the likely death of wife/mother Margaret Gaitens in 1873. jmara, you could check that death to see if this is Thomas' mother's death. Death cert will include lots of details to let you confirm it is the correct death. There is also a possible death in 1870 for a Margaret Heenan, going by the age (under 1) possibly the one you found, aghadowey, born in Tradeston in 1870 (death also shows in Tradeston, Glasgow).
jmara, your ancestor I think is Thomas? Did he go to the US? I can see one Thomas Heenan in Illinois with approximate birth years linked to the one in Glasgow. Is this your Thomas Heenan?
Monica