My dad tells me he has a crush on my 14 year old sister

My pet is sick, so He hopped onto my Minecraft to send me a screenshot of her training my pet. I see that he is logged onto his second account, which has kids mode enabled. I look at his friend list, and I see my 14 year old sister on the friend list. I type a simple hii, which autocorrects to hi!, but he tells me "you shouldn't talk to me like that" and then adds "I have a crush on you". I pretend that I don't know it's him and friend him back, and my sister accepts. My heart is racing, I dont know what to do. I tell my other sister to delete her account, but she begs me to keep it. I dont know if i should tell mom but i don't want to ruin Christmas. I'll keep you guys posted, and thank you for watching my stream irl!