I found an entry for James Brewer of Callaway County intermingled with a James Brewer of St Francois County. In this file he has a oath and Bond of $2000 to be released from Gratiot July 5th 1862. This record is in the Union Citizens file and he is always listed as a citizen. No Military service or rank is mentioned. https://www.fold3.com/image/286855775

He has a BLM land grant SW of Fulton close to Portland issued in 1853.
https://glorecords.blm.gov/details/patent/default.aspx?accession=MO0920__.345&docClass=STA&sid=mpzdtuth.0zz#patentDetailsTabIndex=0

1860 census
Name: James Brewer
Age: 48
Birth Year: abt 1812
Gender: Male
Birth Place: South Carolina
Home in 1860: District 18, Callaway, Missouri
Post Office: Reform
Dwelling Number: 110
Family Number: 113
Occupation: Farmer
Real Estate Value: 2000
Personal Estate Value: 1000
Household Members:
Name Age
James Brewer 48
Eliza Brewer 37
James Brewer 13
Matilda Harison 17

Reform MO is here https://www.google.com/maps/place/Reform,+MO+65067/@38.7997919,-91.921027,11.53z/data=!4m5!3m4!1s0x87dc7cf61dc778cd:0x1f54ddf359480fe2!8m2!3d38.7653202!4d-91.779065

This entire Brewer clan just disappears after 1860. I can't find additional census record for 13 y/o James not Eliza. Matilda Harrison may have ended up in Miller county but I can't prove its the same person.

Roberson I have not found yet though there were a number of Roberson's in Ralls and Marion County.