If I recall, the father's occupation for Felix fits - a Traveller and I was thinking they may have travelled around before settling but that is just a thought.
The writing is difficult in 1851 and hearing and spelling maybe not so good

I interpreted Margaret’s birthplace which looks like ‘Dromante’ as Dromintee.
The parish of Dromintee is quite a distance from the parish of Armagh where that birth of Margaret Murphy is recorded and then there is the distance between Donegal and Armagh so it is not easy. There is also a lack of records for that time.
Lastly, I wondered if Andy could be Annie or similar (misheard or spelling).
There is a Preston marriage for Ann Rogers and Patrick Farrell 1851 so they should be on the census but I can’t see them. Again just a thought.