I reckon the fastest route from the UK be either SU or BD/UN flights. SU is better service and newer planes, flying BD/UN will give you shorter connection time and save you from hassle of changing from SVO F (voted worlds worst airport) to SVO D (new SU terminal). Total flying time is around 4 hours on LHR-MOW leg and 8 hours on MOW-USS leg; i.e. 12 hours + 2-3 hours layover.

There are daily flights from ICN (2,3,6,7 with HZ departing 1 pm and 1,4,5 with OZ departing 9am). So I reckon best route for your friendsin the Western US would be LAX-ICN and ICN-UUS. Not sure if you can book it on one PNR. This would be 13 hours on LAX-ICN + 3 hours on ICN-UUS leg; 16 hours +2-5 hours layover.

Your friends in the Eastern coast would probably want to consider flying via Moscow - (SU or UA/UN) would be a faster route for them.