help me address my STDs please?

Please help! Katleigh is my MOH and advice giver, and she's on vacation, i have no one to help me!

I know that on a formal invite, all kids over 16-18 get their own....my STDs are informal postcards.
so on the save the date, can i just list eveyone, even if they are adult children, like in their 20s?

like if Michael is 20 and Jane is 22 yrs old, can i do this?

Mr. & Mrs. J. Smith
Ms. Jane Smith
Mr. Michael Smith
123 Avenue Street
Town, ST 12345

and with young children (one cousin has 5 kids under 10 yrs!)
can i say
Mr. & Mrs. J. Smith
and Family
123 Avenue Street
Town, ST 12345

your ASAP replies are much appreciated.
lp

STD, I think we just did The Smith Family regardless of age if they still lived at home.

for just a married couple I think we did Mr. & Mrs. Smith