hexproof can't be the target of spells or abilities controlled by that permanent's controller's opponents or by that player's opponents, as the case may be (C.R. 702.11b-c).
shroud can't be the target of any spells or abilities, no matter who controls them (C.R. 702.18a).
However, the first mode of Sakashima's Will targets only an "opponent" and its second mode doesn't target anything (C.R. 115.1a). Thus, you can cast Sakashima's Will even if every creature on the battlefield has hexproof or shroud, but can't do so if all your opponents have shroud and/or hexproof and you choose the spell's first mode or both its modes (C.R. 702.18a; 702.11b-c, 602.1c, 602.1). Moreover, if an effect grants shroud or hexproof to Magda, that ability generally won't carry over to any copies of Magda with Sakashima's Will (C.R. 706.2). Remember, just because a spell or ability has a player choose one or more objects (such as a creature), that doesn't necessarily make them targets of that spell or ability (C.R. 115.10a, 115.10). See also this thread, this thread and this thread.
What effect would this have if I play Sakashima's Will using it to make my creatures become a copy of Terror of the Peakswhile having one of the previously mentioned affects on Magda, Brazen Outlaw
However, both affect *targeting* and the second mode of Sakashima's Will doesn't target so it wouldn't be hindered by either one.
However, the first mode of Sakashima's Will targets only an "opponent" and its second mode doesn't target anything (C.R. 115.1a). Thus, you can cast Sakashima's Will even if every creature on the battlefield has hexproof or shroud, but can't do so if all your opponents have shroud and/or hexproof and you choose the spell's first mode or both its modes (C.R. 702.18a; 702.11b-c, 602.1c, 602.1). Moreover, if an effect grants shroud or hexproof to Magda, that ability generally won't carry over to any copies of Magda with Sakashima's Will (C.R. 706.2). Remember, just because a spell or ability has a player choose one or more objects (such as a creature), that doesn't necessarily make them targets of that spell or ability (C.R. 115.10a, 115.10). See also this thread, this thread and this thread.