Also, for both, you might contact the County Clerk and or the State Archives of the state where they were living at the time the war broke out and possibly obtain their enlistment information if you have the ASN's.
And to possibly find out the last unit they were in, do the same but also contact the state where they lived after they got out of the service as they may not have returned to their home state.Hopefully in one of the two places, they registered their discharge papers.
Also, if they survived the war and collected VA benefits, the VA may have information.
Also, if they have passed and had a military funeral, contact the Sexton of the Cemetery where they are buried and/or the funeral home that handled their burial as they may have some information.
And if they belonged to any military veterans groups like VFW, they should have some information.