Yes, if they are moving in together, they can attend the same appointment and fill in a single Anmeldung form. The same applied to families. However, if the situation is that they are an unmarried couple or friends, then a separate appointment would be needed
Note: If one spouse already had a German address and their spouse moved into a new apartment with them, but did not previously live at the same address, separate Anmeldung forms and separate appointments may be required.