Some of us are blessed with large families; on the down side, some of our family members don't live close enough to visit frequently. Little ones forget names (and sometimes faces) between visits.
Our solution is mini-picture albums.
Get a couple of those pocket-size picture albums--you will want one for each child. Gather up photographs of distant relatives, or close relatives who live at a distance. Use a permanent Sharpie to label each picture on its transparent sleeve, including relationship to the child.
Once or twice a week, take your little one on your lap and page through the mini-album. Tell stories about each person. Little ones love to hear the same stories over and over, and the stories will provide a "hook" for remembering who the various family members are.
When you see the relatives in person, you can remind your child, "This is Aunt Maude, who makes the best pineapple cake in the world!"
Or, "This is Uncle Jerry, the one who got bit by the chipmunk!"
The kids will feel more comfortable, because the names, faces, and stories are familiar. The relatives will love knowing that the babies they love so much are learning who they are.
Just be sure that the pictures are reasonably up to date, and actually look like the people.
It works for me. Let me know how it works for you.
P.S. The reason you need one for each child is that the older kids won't want the babies to slobber on *their* book. This is according to Emily (4), who doesn't want baby Will to slobber on her book.