If a creature is goaded, it "attacks each combat if able and attacks a player other than the controller of the permanent, spell, or ability that caused it to be goaded if able" (the latter player is who the creature is "goaded" by) (C.R. 701.38b). For Martial Impetus, the creature is goaded by Martial Impetus's controller. For a spell or ability that "goads" a creature, the creature is goaded by the controller of that spell or ability, until that player's next turn (e.g., for Jeering Homunculus's enters-the-battlefield ability, that's whoever controlled Jeering Homunculus when it entered the battlefield [C.R. 113.8]) (C.R. 701.38a).
The preceding paragraph applies even in Two-Headed Giant (and other game variants that use the shared team turns option), where creatures still attack individual players or planeswalkers (under current rules, they don't attack teams in such variants), and the goad effect restricts this choice (C.R. 810.7, 805.10b). See also this thread.
Note that the rules for the goad keyword don't use the word "you" (review C.R. 701.38), but even if they did, nothing in the rules for the Two-Headed Giant variant or the shared team turns option changes the meaning of "you" (review C.R. 109.5, 810, and 805, especially C.R. 810.5)
EDIT (Nov. 15): Edited.
EDIT (Jul. 22, 2021): Edited to conform to rule update with Adventures in the Forgotten Realms.
Which person does a goaded creature attack of team 1: player A or B? Or not all?
Thanks for the help.
The preceding paragraph applies even in Two-Headed Giant (and other game variants that use the shared team turns option), where creatures still attack individual players or planeswalkers (under current rules, they don't attack teams in such variants), and the goad effect restricts this choice (C.R. 810.7, 805.10b). See also this thread.
Note that the rules for the goad keyword don't use the word "you" (review C.R. 701.38), but even if they did, nothing in the rules for the Two-Headed Giant variant or the shared team turns option changes the meaning of "you" (review C.R. 109.5, 810, and 805, especially C.R. 810.5)
EDIT (Nov. 15): Edited.
EDIT (Jul. 22, 2021): Edited to conform to rule update with Adventures in the Forgotten Realms.