L.L.
Especially with religion, as long as the effort to understand is there and they are memorizing what you want them to, that should be the standard. However, I don't know why you'd have trouble grading science and history...those ARE absolute, as far as "facts" are concerned. (I personally teach science from the creation viewpoint, so we learn a little differently.)
When I was doing my own grading, I honestly looked at my daughter's overall efforts and overall achievements. I also used tests as a standard. I did grade each worksheet/assignment, etc, but it was easier because mine was younger when I was doing my own grades. Now we're doing online school and I am not responsible for deciding her grades! What a relief! :)