You want their read on Sunday lunch versus Saturday dinner, because half their side travels and they know who will actually come. They are not in the couple's chat. They will not scroll a binder. They will open one email in the morning and answer one question if it looks like one question.
Ask for that. Then stop.
One question, why them, two options
Respect their time. Open with the ask: "We want your opinion: Sunday lunch or Saturday dinner for your side." That is an opinion. You still decide. You want the people who will sit at those tables to say what is true.
Give the constraints a cold reader needs:
- the two times, and which relatives are already committed
- the travel problem you know about (the cousin who will not fly on Saturday)
- why their view is the one you are missing
Leave the rest of the binder off the page. They do not need the florist, the song list, or your assistant's seating simulation. If a sentence exists to impress them, cut it.
A sufficient reply is a lean and a reason. "Sunday, because the travelers will still be here." That is complete. "Happy with whatever you choose" is also complete — and useful, if you asked for an opinion and not a decision.
They read email. They need nothing else.
Writing to someone who is not on RelayLink is the default here. The briefing is a notification and a link. No account. No assistant. No password — if they ever sign in, it is an emailed code, and that is their choice, not a requirement for weighing in.
If they already have an account, you need an accepted contact first. Do not treat a contact request as a prerequisite for asking about lunch. Most in-laws will never have one.
You still approve the send. The session may contain your unfiltered read of their last visit. That read stays.
Do not make them the family referee
You asked about lunch. You did not ask them to settle the thing with your parents, or to "talk to" a sibling. If the briefing smuggles that job, you have handed them work they did not take, and they will either dodge the whole message or take a side you cannot put back.
If they want a call, they will say so. Send the written question anyway. The call then has a spine, and you can write the answer on the thread so the next planning session does not invent what they said.
A reply is how you know they have it. A fetched link is not a read. You will not see whether they have already told the travelers. When the next question is sitting in a session, connect your assistant and send one input request, not the binder.