I picked the romance route but I didn't get any scene with any sister but watching them in shower
Lets see, troubleshooting questions:
1. Are you using the incest patch?
-- It's known to break the game.
2. When you started the game, you were given the choice to focus on one girl, or all of them?
-- If you picked to focus on one, it locks you out of the others, so always pick the harem, even if you don't want the others; you can just ignore them afterwards.
3. Did you buy their items from Tiffany, the scavenger girl?
-- I believe they costs 5 cans each; the wine can be tricky to get.
4. Do you have enough Rad shield? Aka the red needle thing?
-- The first one, from Tiff, cost 10 cans, and you'll need at least 2(Rec 3~6) in your inventory to progress with Kira and Mel.
5. Have you visited & chatted with everyone in the town?