I agree with Geeta. We've seen people on here who have, for example, needed to return to the US to finish selling a house or tie up loose ends in a job after having officially moved to the UK. As a UK citizen, there is nothing stopping the sponsoring spouse from continuing to work for a US employer, even if that requires them going back for a couple of months to do something in person. The reasons for them making the move in September are obvious for the children to start school on time, and as long as the UK spouse is arriving with them at the start of the visa and they meet the requirements otherwise, I don't see how this is a problem or a deception.