How should I word my request line?

Two phrases are the most traditional; one indicates the ceremony will be in a house of worship, the other that it will not. But informal wording is becoming very common. Just be sure that whatever phrasing you choose indicates that guests are being invited to a wedding ceremony or the reception only.

Ceremony at a Place of Worship
request the honor of your presence

Ceremony at a Secular Location
request the pleasure of your company

Informal Ceremony
would be delighted by your presence
at the marriage of their children

Informal Reception Only
invite you to join them
at the wedding reception of