What does this mean: "My research - no IRS limit for a separate return"

Of course there is a limit. If this person has no policy, they are not entitled to an HSA contribution deduction and any contribution made into the other's HSA account is from the spouse that has the coverage, and that would be an allocation from that spouse's limit.

"So should be okay to override line 6, right?"

Did you mark the Right Return as the person having the Policy? One Family, one not at all.