Does Alf work in the Infinite Library?
The two familiars that you mentioned, Aria Liese and Lotte Liese, were helping at the explicit request of Yuuno. They did not work in the Infinite Library at any given time, other than that moment. Due to Yuuno's extreme effectiveness at organizing documents in a pile of organized junk, he was invited to become the head librarian.

Arf was no working at TSAB during the StrikerS period, as mentioned in the sound stages. According to that, she primarily spends time at Earth babysitting. I do not know of a reference that links her to the Infinite Library, other than appearing once in StrikerS. She might have been there to visit for all we know, but it might be something part-time as well.