I hate to burst your bubble, but you're definitely not a direct descendent of Thomas Ashe's. Not unless you're descended from a illegitimate line, but I've never heard of one. He may have had a nephew, Thomas, from whom you are descended.
Thomas was born to Gregory and Ellen Hanifin, in Kinard, Co. Kerry. It's on the Dingle. There was no Irish Republican Army, per se, in 1916. They were the Irish Volunteers. Thomas was a Commandant under James Connolly. He knew Michael Collins, but as far as I know, did not serve under him in the Volunteers.
I recommend you try and get your hands on a copy of "I Die in a Good Cause: A study of Thomas Ashe idealist and revolutionary" by Sean O Luing. It's probably the best book written about Thomas Ashe.