HELP! Question about addressing invites...???

FH has many cousins, some who are younger then 16, some older then 16. The ones who are younger then 16 we want to include in their parent's invite, but how do you word the address if they have like 3 kids under 16. The ones older then 16 are getting their own invite. I do not want to say 'mr and mrs so and so and family', but not sure if it would be tacky to say 'mr and mrs so and so, billy, bob, and thorton'? What is the correct ettiquette?

I just photocopied the etiquette according to Crane's on wedding invite addressing.

Outside envelope should read:

Mr. and Mrs. John Smith

Inner Envelope should read:

Mr. and Mrs. Smith
Mssr. Michael Smith
Mssr. Andrew Smith
Miss Emily Smith
OR

Mr. and Mrs. Smith
Mssrs. Michael and Andrew Smith
Miss Emily Smith

children should be listed in chronological order starting with the oldest.

i wrote on the outside: Mr. and Mrs. John Smith

and then on the inner: John, Susan, Sophia, Isabella & Gabriella Smith