Anthony, in line with prior comments on one or more of your other abundant posts in the post week or so, some of these individuals may be living and I do not believe it is appropriate to seek details on them on this forum. Your repeated queries seem to point towards a desire to identify living family members rather than trace backwards.
Regarding Martin, a simple google search gives an entry on RIP.ie, an Irish Times entry and information from his show band career.
In relation to his siblings, the only records you would find for people of this generation to my knowledge would be indexed BMD records that cover the period to 1958. These are only available on Ancestry (unless someone else knows different) but would only have the registration location and mother's maiden name along with the year and quarter. There is obviously the possibility of multiple O'Rourkes being born to Phelan mothers with those forenames and if you do not have dates you might come up with a lot of 'hits' to follow up on.
There are a lot of free resources that will cover the period until 100 years ago for births, 75 years for marriages and 50 years for deaths and Jean has referred to some of these in her answer already.
For people that have passed away recently (i.e. in the past ten years or so), sites like RIP.ie would have death notices.
