*Huge fan of The Sims here, too!*
Sexy Sims 2 was a blessing and a curse at the same time, lol. It was after finding this thing on that site that I decided to give my try at modifying stuff myself to make Blackie Lawless' assless pants. Been going crazy on a TS2 Blackie Lawless sim for over a year, as well as 80s rockers in TS3, lol.(Here's the infamous Blackie outfit I made and here's a not-so-recent and absolutely-non-definitive version of the sim )
[/end shameless self-promotion]
Never downloaded any of the sexy mods yet, though!
Even if I was thinking about installing them lately
Unfortunately, I think there's no way to make your brother not notice those mods
the objects will appear among furniture stuff, clothes will appear among normal clothes and the new interactions will just show up directly on the sims, as well as stuff like penis and bigger boobs
unless someone made a mod to hide particular objects when a certain user is playing the game, but I don't think there's anything like that D:
Buuuuut... a sort of solution -at least for stuff that involves interactions- could be installing poseboxes, instead? Most of them don't offer animations, though, just the still pose... but you could put them in game and they would appear just as boxes, in most cases with pose names in English, and sometimes will be totally non-descriptive names like "pose 1" and "pose 2"
For someone who doesn't really know the cheat and codes to place sims and move 'em around to make them fit the right positions, most of the poses coming out of the 'sexy' boxes wouldn't make much sense and you could be safe
-Here and here for couples, not even that much explicit. Another one by the same author is here
-And here's a looooooooooong list of other poseboxes. Haven't checked them all, but I'm pretty sure there are some other ones for sexy poses.