Spam from the same address will appear as a single chat, and you can block the contact and never receive more spam from that address
Since spammers constantly change address you might what to tweak the "show classic email" option in Advanced settings, if you set it to "accepted contacts only" only classic email from contacts you have accepted a chat already will show up in Delta Chat so contact requests from new contacts will no show up, which is perfect if you only want your dad's messages to appear in the app
My personal experience: 121 chats (just my family account I have several other accounts)