Not cleanly. Reps has a single library per copy of the app, with no profiles and no user switching, so two people sharing one installation would share one set of classes, one due count and one schedule.
That arrangement fails quickly. Spaced repetition works by scheduling against one person's memory, and a shared library has no way to tell whose memory answered.
Separate devices on separate accounts. The usual arrangement for siblings, and the only clean one on iPad. iPadOS has no general user switching, so two people cannot keep separate libraries on a single iPad.
Share the material, not the library. Export a subject as a .reps file and send it. The other person gets a copy of the cards in their own library, and their schedule is built from their own answers. This is the intended way for two people to work on the same material.
macOS user accounts work as you would expect. Each account signs into its own Apple Account and gets its own Reps library.
A Universal Purchase covers iPhone, iPad and Mac for the same Apple Account, so one person does not need to buy it repeatedly.
Reps also supports Family Sharing. One purchase covers everyone in your family group, each on their own Apple Account with their own separate library. For siblings studying different subjects, that is the arrangement you want: one purchase, one copy each, no shared due count.
More answers on the help page, or write to [email protected].