I found the parents of Alexander Ross on family search:
Helen Lamb, About 1807 Of, Meigle, Perth, Scotland
Alexander Ross, About 1803 Of, Meigle, Perth, Scotland
CAUTION! the fact that the parents are said to be 'Of' somewhere is an instant warning that the information is 'submitted' to the IGI, so just like 'Of Gleish' it must not be taken as reliable. It will be the usual LDS educated guess.
I couldn't find a date for their marriage.
Alexander Jr is the only child of this couple. You cannot find a marriage record. He is with his grandfather in 1841. I therefore surmise that he is illegitimate. Of the three IGI listings of his baptism, one is 'extracted', so you can look at the image of his baptism at
www.scotlandspeople.gov.uk - I bet it tells you he was born out of wedlock.
Then, somehow, before 1841, he ends up in Newtyle: a village of less than 1000 people, with a family of 'Lamb's.
Newtyle is the next-door parish to Meigle, even though they are in different counties. The villages are about 2 miles from one another.
My conclusion is that he is probably a relative to my own Lamb ancestors, his mother's maiden name Lamb and his presence in another Lamb family is too much of a coincidence for him not to be. I will have to find out exactly how he is related though further research.
I agree, and I am sure that his mother Helen will turn out to be Marjory's sister.
To prove this you would have to hope that Alexander Jr either married or died in Scotland. If so, his marriage and/or death certificate ought to give his mother's name and with luck her married name (assuming that she did in fact marry). Then get her death certificate and see what is says her parents' names were.
Another possibility is that the Newtyle and/or Meigle Kirk Session took an interest in the birth of Alexander Jr and that the Kirk Session minutes say enough about his parents to let you identify his mother. The minute books (if they have survived) will be in the National Archives of Scotland
www.nas.gov.uk but they are not (yet) online so you will need to get someone to look them up on your behalf.