What is the Ashkenazi custom for Aliya La’Torah where no Kohanim are present and there is more than one Levi who are close relatives of a Bar-mitzvah – can more than one Levi be called to the Torah?
The custom is that only one Levi is called up to the Torah, for the first aliyah (instead of the Kohen).
This itself is the subject of a dispute among poskim (see Rashi and rishonim, Gittin 59b), and see Shulchan Aruch and Rema 135:6 (a Levi can be called up first), but see Taz and Bach (a Levi shouldn’t be called up at all). It is customary to not call up more than one Kohen or Levi (Magen Avraham 135:16, citing from Levush; Mishnah Berurah 36; Shaar Efraim 1:17).
A second Levi can be called up for acharon (after the seven regular keru’im), and also for maftir.