Sailed on 'Sir Thomas Lipton' out of Ullapool

My grandfather John MacDonald, sailed on the 'SirThomas Lipton' out of Ullapool. He was a twin and his family lived in Ullapool.He had nine brothers and sisters, and that's all that I know. His mother was the post mistress for a while in Ullapool though I don't know if that was before her marriage. Iwonder did his twin die at birth or in early childhood? He came to Ireland eventually and my dad was born in 1912, the first of three, the others William and then Kenneth. My granda died in the 1960's in his early eighties. Any clues would be great.Thanks