When I needed that (and more) I created folders.

The setting was a detective kind so it suited perfectly. Inside I mapped relationships using polaroid like pictures with cards: Had a picture of the person on the first page, on further pages I had pictures with relationships as a list of cards with stuff like "hates due to betrayal" (and stapled details in case I forgot) or "possible romantic relationship (unconfirmed)" color coded.

What You could do is a similar thing except less modern and with sketches instead of pictures.

I would keep all folders in our usual play place under a lock in my desk so whenever I needed any information I'd open it and look through.

Worked well.

When I needed that (and more) I created folders.

The setting was a detective kind so it suited perfectly. Inside I mapped relationships using polaroid like pictures with cards: Had a picture of the person on the first page, on further pages I had pictures with relationships as a list of cards with stuff like "hates due to betrayal" (and stapled details in case I forgot) or "possible romantic relationship (unconfirmed)" color coded.

What You could do is a similar thing except less modern and with sketches instead of pictures.

I would keep all folders in our usual play place under a lock in my desk so whenever I needed any information I'd open it and look through.

Worked well.

EDIT: As per comment:

If You want to have access to all the characters at all times and your information amounts are relatively small, You could try making a wiki with it and use a tablet/phone as an aid behind your GM screen.

This is what I did for my SF scenario. (admittedly very short lived due to group dissolving, only three sessions) Images link to character pages and there you have a list of images with relationships.

Since it was only three sessions, it was a very small wiki and I have no idea how (and if) that scales. Theoretically should though.