D.
Have you seen the Family Tree on Ancestry for a John McTimoney -- or is that your tree? He was supposedly born in 1834 Belfast, with a father James b 1799.
There is an entry in the British Army records for a Jas Timoney. Unfortunately it's just an entry in a Pension book dated 6th Nov 1842 giving this Jas an age of 43 - born in Dromahain? Leitrim. No other useful info for him. He was leaving the Army presumably with a pension, due to a persistant cough.
Neither your John nor David are coming up in Army births.
Pennines
I'm very wary of taking the contents of any Ancestry tree as 'truth' because so many of them are wrong. [I'm a professional researcher/biographer in another field, and it makes me hyper-careful.] I think using Ancestry is an enjoyable hobby for many people (and why not), but they often don't trouble to back up their 'finds' with records or proper evidence, and the trees fall apart as soon as you go in deeper.
I've been in touch with a number of owners of Timoney trees, who have supplied more info. than you can see on Ancestry online. The James Timoney/Tumney [6th dragoons] would be a very good bet in many respects, if only there were a solid record for a son John. Sigh.
My John's first son Henry was desperate to join up with the dragoons in the 19th century - why? Nobody can say. Henry managed to get himself into the Hussars, light infantry. Why was he pulled this way? Something in the genes?
We also know of a 19th century 'Uncle Jimmy, who fights'... so who was he?
Do you know any unconventional ways of busting through seemingly impossible blocks?
D