Okay, so lemme make sure I got everything understood:
There are 2 games in this series. The first one is called Rape of the Dead. It features 3 girls: a rich, green-haired loli wielding a minigun and wearing a crown, a redhead with a blue flower hairclip in her hair wielding a machine gun, and a busty, black-haired office worker oneesan who wears glasses and wields a shotgun. When they made an official English translation of the game (I don't know if there was ever a fan translation of the first game) they changed the name of the game to Seed of the Dead. This was probably because of the whole Rapelay debacle still looming over eroge in the Western market.
After Rape of the Dead (or Seed of the Dead), Team Kramer made the second game Seed of the Dead:Sweet Home. That is this game. This game features the 3 girls from the previous game plus one new girl, but with a few changes. The redhead now has her hair closer to a shade of pink and her hairclip is a bit more detailed. The loli got yellow hair and lost the crown in return for some black bunny-ear hair ribbons on the base of each of her twintails. And the busty oneesan-type had her hair turn bluer (though it may still be considered black, and the "blue" color is just there to be a sort of "stylized" black hair color) as well as a red ribbon at the base of her ponytail. The new girl has light purple hair and wears a hoodie while wielding a sniper rifle.
The developers are making a DLC for Seed of the Dead:Sweet Home called...Seed of the Dead:Idol Days. It will be a continuation of the story and will include a new character. I don't know any more information because I can't find the website for it. I don't know if it's going to be an fps zombie shooter like everything else or if it's going to just be an idol management game.
Is that everything or is there something I'm missing?