No, the Abbotts are not my line, I just give out suggestions for research.The marriage of FM to Melissa may have been a 2nd marr.Or, this may be a different FM Abbott.Obviously FM & Emmaline were married prior to 1882 when Shelby Co, TX marriage records begin.Funny, Sanders book doesn't give dates covered for marriages.Emmaline & FM would have been made prior to 1877 when Cuthbert died, and she was appointed guardian.
You need to look at Orphan Court and Guardianship records for Crawford Co, GA.Also, probate, and land records.You may find out more about Cuthbert in those records.Guardians could be appointed even if the mother was still alive.That's why you need to look at other records, too.If you look at birth years for the children, all of them were "of age", except Richard and Marion, that's why they had guardians appointed.It is strange Emmaline, the aunt by marriage, was appointed the guardian.
Yes, I know you don't know Lucy's parents names, but thought you might find a couple that fit date wise, and could check them out.When did Lucy die?Don't you have a death certificate for her?It should have the names and birth location of her parents on it.
Have you looked at the 1870 census when Cuthbert was still alive?That should give you approximate birth year for Richard.
As to what happened to the siblings of Marion, my guess is the older ones stayed in Crawford Co, GA, and the girls may get married there.And, your info shows Richard in TX.
You have some good information on your family, just hang in there and keep plugging away, you'll find more, I'm sure.