If you're willing to pay up to $2500 per passenger per ticket (assuming this $2500 is cash on top of the miles), you could try paying for Premium Select seats to Seoul (only works on Delta metal, wouldn't work for other destinations since Delta doesn't fly there) and then using Mileage Upgrade Awards to upgrade to D1. From Premium Select to D1 it's a fixed amount of 45K miles each way, so 90K miles plus the ticket price. I'm seeing PS for nonstops between SEA and ICN for ~$1500 for most dates in 2022 (I was able to find it around $1200 pre-pandemic), so this would come out to 270K skymiles for 3 passengers, plus the ticket prices.

To add, this may not be the highest value you can get from miles but it meets the criteria you're looking for. I've completely given up on finding full award tickets myself and use MUAs with PS tickets so I can accrue some MQMs and MQDs on the trips.