Hi Tom,
I'm really happy about your invitation to your parent's cottage. But I must explain to you, however, that at on the same weekend, my cousin, John, is come coming from Italy to visit me and I couldn't throw turn him by away. I have known him all my life and he would be happy if I spentd the weekend with him. I want to tell him about, and show him all the interesting places in our city be like: Freedom Square,The Zoo, Theater of the Young Spectator, the seafront.
Of course I want to visit the amusement park and enjoy all the attraction sites. In my opinion, he will be very happy and enthusiastic. If you want to join us, you are always welcome!

Best Wishes,

Mary

Hi Tom,
I'm really happy about your invitation to your parent's cottage. But I must explain to you, however, that at on the same weekend, my cousin, John, is come coming from Italy to visit me and I couldn't throw turn him by away. I have known him all my life and he would be happy if I spentd the weekend with him. I want to tell him about, and show him all the interesting places in our city be like: Freedom Square,The Zoo, Theater of the Young Spectator, the seafront.
Of course I want to visit the amusement park and enjoy all the attraction sites. In my opinion, he will be very happy and enthusiastic. If you want to join us, you are always welcome!

Best Wishes,

Mary

Hello. I apologize because I see I uploaded two corrections. They are the same so you can ignore one. 
It's a very nice and well-thought out entry. If you have a question, feel free to ask. 
All the best!