Questions about a thank you card

I am writing up my thank you cards. I invited a friend of mine and her husband (Jenny and Robert), but I didn't invite their kids. The kids (Tony and Steve) are adults in their twenties. I knew them, but wasn't close with them and couldn't afford to invite them.

But the wedding gift that I received from them was signed Jenny, Robert, Tony, and Steve.

How do I address the envelope and thank you card? I have been thanking people for attending the wedding, or expressing sadness that they couldn't come. So what should i write on the thank you card? It just feels weird b/c Tony and Steve weren't invited.

TIA

I'd address the card to the people you invited and that attended - don't worry about who's names they signed on the card