It should be a brief letter to invite the family and friends to join in your happiness. Use very simple language and be specific about the date time and venue to avoid confusions. Since it’s the 25th anniversary to celebrate a couple’s togetherness convey that enthusiasm and joy in your letter
Dear Name,
Please join us in celebrating the 25th anniversary of our parent’s __________ and __________.They have been together from past 25 years and has raised a family had a very happy married life till today.
They have been together in all these years and have seen all the ups and downs together .we would like to make this function a special one for them. We request you to wear _________ as this would be the dress code of the party.
Since you all have been a part of their lives please come and have your presence on _________ (date) at __________ (venue).
Yours sincerely,
Your name