Unless it says a specific accommodation for his family, $8.00 per month means $8.00 per month (although he actually may have been paid $24.00 quarterly.
(That's small but maybe not as small as it seems. $8.00 in 1863 would be worth $183.27 today.)
The actual amount of each pension check is recorded on Page 2 of a veteran's record in the "United States Veterans Administration Pension Payment Cards" database on
FamilySearch.org.
(The same database is on
Fold3.com and other places but Fold3 only shows you Page 1 so you don't see the individual payments).
For more information about these versions of the database see my blog
HERE.