Adult only. Private by design.
How to approach another couple

You are already on the list. A hello is a sentence, not a pitch. Ask once, then wait for their answer.
The short answer
Approach another couple the way you would greet friends of the host. Names first. One sentence about what you are open to. Then stop talking and let them answer.
Your host invites friends. The host invites friends they'd love to have there. You are not working a public room. The other couple is here because the host wanted them, same as you.
Adult only. Private by design. You confirm you are 18 or older. The host still checks you in.
How a hello goes
Short is kinder. They can always ask you to say more.
- Greet the host before you greet the room.
- Use the names on the invite. Skip the story about how new you are.
- Say what you are open to in one line: talk, watch, soft, or full.
- Ask once. A pause is their turn.
- A no ends it. Thank them and stay where you were invited to be.
The ask
A clear ask sounds like this: we are here to talk, or we are open to a soft night if you are. It does not sound like a speech, a joke that hides the ceiling, or a hand on someone who has not answered.
If the house rule is softer than what you wanted, the house rule wins. Do not negotiate a fuller night in the kitchen. That is a different party.
Message host if you are unsure which rooms are open. That note stays with the host. It is not a side chat with the other couple.
When they say no
Thank them. Go back to your drink, your partner, or the couch. Do not ask again later in the hall. Do not tell the group chat. Do not follow them into a closed room.
If someone will not hear your no, or you will not be left alone, tell the host. Then leave with your partner if that is what you need.
FAQ
Do we introduce ourselves as a couple?
Yes. Say both names. You are two guests, not a single person shopping the room.
How long should the hello be?
A few sentences. Names, then what you are open to. They can ask for more.
What if they do not answer right away?
Wait. A pause is an answer in progress. Do not fill it with a second ask.
Can we approach a couple we were not introduced to?
Only if they are on the host's list and the room is open for that. If you are unsure, ask the host.
What if we only wanted to talk?
Say that in the first sentence. Talking can be the whole night.