You are not causing any 'trouble', heilanlassie 
From reading through, my first thoughts are that Alexander was likely sent to live with family in Ullapool you would think after the deaths of his parents in the 1860s (I know you have still to find their deaths at this time). Specially with the earlier mention of a sister to Philip, Kitty McCree, living in Ullapool in the 1830s.
Mary McCree, mother to Lexy. What do you know about her? When was she born? Did she die after 1855 to let you check her parentage?
Monica
Thank you Monica.
I first find Mary Macrae (spelt this way) on the 1861 census, as head of the house in Market Street, Ullapool, stating that she is 80 years old, unmarried and a pauper.
Also in the household is Lexy Mackenzie, unmarried, daughter, aged 30, a domestic servant.
Also in the household are two visitors, Janet Mackay, unmarried, aged 30, pauper and Eppy Ross, widowed, aged 80, pauper.
On the 1871 census, Lexy Mackenzie is the head of the house in Market Street, Ullapool, unmarried, aged 40, domestic servant.
Mary Macrae, mother, single, aged 60, pauper.
Also in the house is Alexander Macrae, nephew, aged 16, scholar.
And Roy MacDonald, lodger, unmarried, aged 60, pauper.
Mary Macrae died on 05 January 1879, in Market Street, Ullapool. She was stated to be 91 years old, single, pauper.
The death was registered by her daughter, Alexandrina, who stated that Mary's parents were Farquhar Macrae, deceased, crofter and Ann Macrae, nee Munro.