I've been having another look- I did find two christenings before for a George Glover (one with father "Johannis" and the other George) but I suspect the one with father George is an error, either in transcription or the original. I can see three siblings at the moment, Mary (1758-1774) Margaret and Anna (who you say became Hannah?)
Part of the problem for me, aside from being somewhat allergic to the evidence "it's the only one I can find", is that none of the names John, Margaret, Hannah or Anne appear in George's family. To make matters worse, I can only find two children for his marriage to Martha so those names could appear among any missing children.
While researching, I did have a look at James GLOVER and his wife Betty in Kendal. I can't seem to link the two families as yet, but it is interesting to note that George's son named his firstborn son James and I've been unable to find any source for this in the rest of the known family.
(Online Westmorland records aren't too great, are they?)