Go to familysearch.org for ancestors of Milton Price Brittain.

Click on Ancestral File. Near the bottom of the page is an area marked "detail" click on that and you will see

BONNIE YORGASON Microfilm: 1394242
411 E DEL NORTE
COLO SPRINGS CO Submission: AF83-054919
USA 80909

LANA J WHITING Microfilm: 1394186
869 EAST 2ND STREET
STEVENSVILLE MT Submission: AF83-041203
USA 59870

MRS. KEITH SWANSON Microfilm: NONE
1408 CHESTNUT
ATLANTIC IA Submission: AF92-105682

See the microfilm numbers? Those are FHL film numbers. Order these films from your local Family History Center. The films will have documented family group sheets for the descendants of Parks Brittain and Sarah Price.

For further descendant generations you should use the federal censuses and postings at genealogy message centers like this one.