If you didn't see the tattoo with the flashlight, the person who bred the goat's sold them with registrations, but did not tattoo. Animals should never be registered unless their tattoos are in place. Alas, a lot of breeders do this. They send off registered animals with blank ears all the time.
So now, it is up to you to either take them back to the breeder for the tattoos to get put in (they have the pliers, herd sequence for one ear, and should have the letter for the year and additional numbers for the other ear) OR purchase the equipment and numbers + letters to do it yourself.
An animal who can be registered should not leave their birth property without the tattoos. Mine never will. Buyers should not have to deal with that. The time and equipment to properly identify animals is just part of keeping registered stock.
Herd tattoos go in the right ear, year letter and birth number (of ALL goats born that year to that farm, not that doe) go in the other. Since you have the paperwork, at least you know the tattoos. Their twins, so they have the same mother and father, easy. One gets one set of paperwork, the other the other. Appropriate tattoos are placed corresponding to paperwork. The birth number will be one different, more than likely, with the girls.