It's been awhile since I've read the manga, so I don't know exactly but I think the line went something like 'when a low class exorcist was possessed by Satan and was impreganted' they were talking about the circumstances of Rin and Yukio's birth.
During Mephisto's trial, they say her name in the manga.
Chapter 14, Page 30, well what do ya know...
In that case I can only assume it was to avoid raising suspicion, since Shiro was supposed to kill them.
Ah that makes sense! Thanks, this has been bugging me for a while!
Lmao, I wonder why nobody pointed out the fact that Rin and Yukio's last name!Es were different from their father's when they were kids or signed in at the doctor's or so where else. Humans are unbelievably stupid in Anime. XD
I think they should have the surname Fujimoto, given he adopted them as his own children. Why did he gave them a different surname, will we ever know?
Well you have to remember, he's a priest and they're orphans. He's not their biological father and, assuming he's Catholic, isn't supposed to be. He's their legal guardian as they grew up in the monastery.