Custom Party from another save

Hey everyone, I was hoping someone could walk me through something real quick. It's been awhile since I've done any modding or been in the DS scene, I can't remember how to add another character from someone else's save to mine. I did it before in both DS1 and DS2, but the process is forgotten to me. I was really hoping to do this because my grandparents may be dying soon and I'd like to play on with their literal memory with there