RSVP card question.. probably a repeat!

Ok, so I broke the 'etiquette rules' and I'm sending an invite per household instead of everyone over 18 getting their own invite. If I didn't do this I'd literally have to send like 20 extra invites.

My RSVP card currently says

The favor of your response etc etc

M_____________________

_ accept with pleasure
_ decline with regret

I wasn't going to put _ Number attending because I thought that would just open up a whole opportunity for people to make a mess and start adding people, etc etc. But now I'm thinking about the families who have 3 kids in their 20's living at home (yes, there are a lot of these) are they going to know enough to write their names, their kids names, AND their kid's guest's names on the response?

Did anyone NOT put the # attending line, and did you have an issue?

Or vice versa?

Or should I maybe print a few RSVP's with the # attending line for those few cases where there would be like 6 ppl responding on the same card?

One solution could be to put multiple RSVPs in the same invitation. For example, you're inviting the Smith Family. Mr. and Mrs. Smith plus their 2 grown children.

You could have one RSVP with 'Mr and Mrs Smith' already filled in the blank, and then add two more RSVP cards for the children's name pre-filled.

It could be a pain, but the only other solution I can think of is just to call them and ask who's coming and who's not.

If I received an invitation like that (me plus my husband and kids all in one invitation) then I would write everyone's name who's attending on the RSVP card.

Some of my guests with children in their late teens/early 20s wrote 'The Smith Family' because they knew that I would know who that entailed. Other people wrote 'Mr. & Mrs. Robert Jones + Katie' to let me know that they were including their 19 year old daughter. One other guest of mine wrote everybody on the back of the card like this:
1. Mr. & Mrs. John Doe--2
2. Michael + Steven (their sons)--2
3. Jake + guest--2
so that I would know exactly how to create the place cards. If you leave it up to your guests, they'll usually figure out the right way to go about indicating that their older children are attending as well.

ok- i guess i dont give ppl any credit lol- i guess i will leave as is and make calls if there is anything questionable!

Based on some stories I've read on here, I just assumed ppl were clueless in general