Invite friends to grandpa's birthday party.

Invite others to your grandpa's birthday party, usually your father will be the inviter.

For example, invite Milla to dinner. Fill it out like this:

To Milla (Miss/Lady/Sir)

Attend my father xx's birthday party.

Date, year, month and day.

Place, somewhere.

Invite people to write your father's name.

Do it.