Q. Can two totally different groups that learned different masechtos join together in one large siyum, or is it like making mitzvos chavilos?

A. Horav Shlomo Miller’s Shlita opiniom is that we do not consider two siyumim done together as chavilos, (packages bundled together, symbolizing that the mitzva is a burden), since they are essentially one and the same mitzvah and we do but one seuda. (see Yomo Tovo Lerabonon p. 300 – In regards to a siyum by a Bar Mitzva, see; Minchas Ytzchok 4:23)

Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit”a