If by 'person's name' you mean the person who the announcement is about, than usually no. If you mean the person who the envelope is addressed to, then also, usually no.
you put the other persons address on the envelope and put your return address on the left corner of the envelope and put a stamp
You dont. Unless the persons live together. If you want to send a letter to some one in Florida and Somone in Texas (hypotheticly speaking) you need to write two distinct letters. sorry!
a tritet
Trio
its called a trio
A Duet
A trio.
3 people singing together would be a trio.
Quartet.
Forget using the attention line. Just put the persons name in the first line of the delivery address.
A quartet
A duet Is what two people singing together is called.