Proper grammar for us and i

I have recieved a letter from my uncle last night and he is inviting me to come and join them to celebrate his third son, the content of the letter is this:

Please! Come and join Us as i celebrate my first birth day -------- . We hope that you can come and join the party!

we debated and open a discussion for this topic and until now we dont know who is correct. Please Answer.... Thanks for your consideration!

God bless this forum!