In a brand new TV documentary, Daniel At 60, to be aired on RTE and BBC NI this Tuesday night, Margo also tells how she prayed that Daniel would learn lessons from the mistakes she made in her own life.
"I had many doubts because I had no easy road in the music business, so I didn't want that for my baby brother, no way," Margo says, looking back at the moment Daniel told her he wanted to leave college and join her band.
Margo's rise to fame had come at a cost, as away from the spotlight she became addicted to drink and prescription drugs.
"Oh, it was hard for all the family," Daniel says. "There's nothing you can do for somebody that's going through that. That's one thing that you learn, that until they are ready there's really nothing you can do. It's a tragedy."
In the documentary produced and directed by Veronica Cunningham, Margo says: "I did a lot of things the wrong way, and I hoped that from me doing them the wrong way he saw what was right."
Daniel says: "I never fell into drinking. Margaret, I've heard her say that it gave her confidence, and I didn't feel the need for the confidence. That doesn't mean that I was always tremendously confident. I wasn't, but that (drink) wasn't where I saw it, so I was lucky."
Daniel and Margo also tell how their beloved mother, Julia, had a huge impact on their lives right to the end…and beyond.
"She was the Rose Kennedy of our house," Daniel says." She was in charge of the whole show."
Margo: "She embedded in him (Daniel) a lot of qualities in how to react with people, and he has followed it through."
Daniel says: "She loved people, she loved the interaction with people, and I wonder is that where we get it from?"
Daniel says that his mother was equally proud of all her offspring. Whenever people would say to her that she must be proud of Daniel, he says her reply would always be: "I'm proud of them all."
Margo reveals that their family found it difficult to gel together after their mother died. "She was such a massive part of our lives and when she was gone it was awful," she says.
"We fell asunder and we said words to one another that we didn't mean, and I'm guilty of that more than any of them. We didn't know where we were because Mam sat on the chair and she ruled the whole family, and what she said went and that was it."
Daniel also speaks about his faith and told how it caused him to have second thoughts about his relationship with Majella at the start of their romance.
"I'm a Catholic and it's good for me, but I'm not going out on stage to tell people what they should do. You can be a good Catholic and not a good Christian," he says.
Majella was a divorced mother of two when they met. "In my mind I thought, how it that going to work?" he says. "And I thought maybe it wasn't going to work. It was probably to do with getting married outside the Church, so I decided that maybe we would part company. And we did."
However, Daniel soon had second thoughts about his decision. "I remember being at Mamma Mia! in London and I was sitting there thinking, 'God, Majella would love this.' I remember thinking then, 'why am I resisting something if it is God-given… it's not given to cause trouble?'
"Getting married I thought, 'well, if God put somebody in my life that gives me joy, why would he do that if that's wrong.' Life is not black and white."
Speaking about his role as a performer, Daniel says he's quiet by nature but becomes a different person on stage. "I think on stage I'm more extrovert(ed). You can't but be affected by the good vibe in the theatre, you get it on the stage. Whatever they get on the floor, we get it back from the audience."
Daniel At 60 takes viewers inside his world on tour. Who knew that the Donegal crooner irons the outfits for all of his band? We also join him on his tour bus, where he sleeps in a bunk, just like the rest of the band and crew on board.
In America, we learn how bus loads of fans roll into Branson, Missouri, to see Daniel perform every year - some travelling eight hours.
One female fan reveals that she tells her family not to make plans in November when Daniel is performing in Branson because she'll be on a trip to see all of his shows!