The website TMZ is reporting that Beyonce and Jay-Z's twins are named :drums: Sir and Rumi. So that would make them Sir Carter and Rumi Carter (Jay-Z's birth name is Shawn Corey Carter).
TMZ noticed that the company that owns the trademarks to Beyonce's and Jay-Z's names, recently filed paperwork to obtain the trademarks on those 2 names.
The trademarks ensure that nobody can sell products that bear those names for the free publicity.
The couple have been very tight-lipped about the new additions to their family.
Rumi is the name of a 15th century Persian poet; Sir, of course, is a title and honorific in many countries and cultures.