If your daughter wishes to have an informal event and only family members are invited, you could design an informal, personal invitation. Perhaps this could even be handwritten. It is entirely your choice.
It could be similar to this: Parent's names (next line) invite you to share in the joy (next line) of the marriage uniting (next line) bride and groom's names (next line) date (next line) time (next line) location (next line) and join us afterward (if reception is another day write the date on the next line) (next line) location. Then follow with the RSVP info.
You could also simply write a personal letter to each of your guests. Just include all of the pertinent information.