Can I put a family crest on wedding invitations?

Yes. Many couples put a crest or coat of arms on invitations, place cards and programs. If one family has official arms, tradition says to show them exactly as granted. If neither family has arms, you can design a new coat of arms for the couple, which avoids borrowing someone else's arms.

A wedding design often joins two families. Heraldry does this with impalement, where the shield is split down the middle and each half carries one family's arms. In the coat of arms maker, the Per pale division gives you the same split,, with a charge for each family on its half.

Put the date or a short motto on the scroll in a font like Cinzel to match the stationery. Then export a transparent PNG or an SVG for the printer, and check the best file format for printing for sizes. The Latin mottos guide has ideas.