Hmm. The sons must have had a variety of names - if John Grant and Eliza were married in 1909 and she hadn't had contact with him for 3 years before 1913, there wasn't time for her to have 9 sons to John Grant unless she had quadruplets and quintuplets in very quick succession!
But it would explain why she wasn't with him in the 1911 census.
On the other hand, if she had Margaret in 1913, it looks as if John b Boharm 1913 can't be hers.
And she was nearly 40 when she married James Gibson in 1926 so she can't have had 9 sons to him either.
I suspect you are stuck with looking for illegitimate Grants, but if you are lucky they might also be registered as Mc(K)andie.
Best place to start is probably
www.cwgc.com but if any of the the sons were indeed illegitimate and known by their fathers' surnames you'll be stuck.