Can you ask Rav Shlomo Shlit’a if someone was Mekabel (accepts) to say a Perek Tehilim for two people, do they have to say it twice or can they say it once and have kavanah it’s for both.

Horav Dovid Pam, Horav Aharon Miller Shlit’a maintain that it depends on the intention of the one who undertook to recite the Tehilim. See also question 67 regarding reciting Kaddish for several Neshomos at once. We wrote: “Many Poiskim agree that one Kaddish could be said for a number of deceased (Rana’ch 1,77 – Gesher Hachaim 1, 326,7 – Kol Bo p.376, Tzitz Eliezer 7,49, et al.). However Igrois Moishe (Y.D. 254) and Doivev Meishorim (2,14) at least partially disagree. The fact that no contracts or monetary rewards are involved in this case is also favorable. Igros Moishe (ibid.) advises that at least one Kadish a day should be dedicated to each Niftar. So too is the opinion of Horav Shloimo Miller Shlit”a. He recommends thinking in advance for whom this Kaddish is to be recited; the rest should be said with the intention for both.”