Dear [name],
It's good to receive your message, sorry for not writing for so long, I have been in the countryside recently, I've been helping my parents there, so I wasn't even able to read your letter.
So I didn't, actually understand, what is common between your passion for reading magazines about celebrities and your party. Anyway, to leave your parents at home or not, it depends what you're going to celebrate at your party. As for me, I would choose something single: to celebrate only with your parents or to have a party with your friends. If I were you, I would choose something single of those. Amount of people to invite to a party always depends on what you're going to celebrate.
Looking forward to receiving your reply with details.
Love,
Rhodion