Q. By the siyum on erev Pesach, is it necessary for the bechor to understand what is said, or do they comply if they are not able to hear or to follow what is said?
A. Poskim disagree if it is essential for one who wants to partake and be part of a siyum to understand what is being said at that time. Ben Ish Chai (Tzav 1: 25), Sidur Pesach Kechilchoso (14: 14) quoting Horav Eliashuv zt'l maintain that it is necessary. Yabia Omer (1: 26: 8) thus explains why a mesechta that end with divrei agadda should be chosen, so that all present will understand.
However, many Poskim maintain that it is not essential and if they attend the seuda they can join with them. (Minchas Yitzchok 9: 45, Oz Nidberu 12: 58, Teshuvos Vehanhogos 2: 210, quoting Horav Kanievski zt"l, et al.). Others maintain that he should at least help in setting the meal.
Horav Shlomo Miller's Shlit'a pointed out that the minhag is to be lenient.
Rabbi A. Bartfeld as advised by Horav Shlomo Miller Shlit'a