Sicae MC has his own exclusive harem. And MBML MC has his own harem.
There's currently none of that NTR shit and there shouldn't be any either.
The Chapter 1 Episode 4 download is the full game.
Discussing the connection between the two games would be massive spoilers, but it is discussed in MBML in Chapter 1 Episode 4 as well as occasionally throughout the rest of the game. The girls in MBML are completely new and don't appear in Sicae at all (they might appear in episodes 6 and 7 but I haven't played those yet, but other than that no. And it'd be cameo appearances just as a sort of "hey I recognize her!" moment.)