Hello! First of all, thank you very much for buying the game, we hope not to disappoint you!
Regarding your comment giving us advice, I will send it to my friend, who is the programmer. Thank you very much for your help!
About the conversation, to unlock both the conversation and other functions, you must increase your relationship level with the girls. You can do this by going to fight monsters taking them with you. To do this, go to the inventory and select the girl you want.