In a perfect world, I'd tell them to start packing for their move now. Begin with the many knickknacks & family photos. Declutter. Simplify. I'd walk thru their home and point out what needed to be in those packing boxes. I'd tell them to look at their home with "buyers' eyes."
We are not in that perfect world though. The photos & mementoes have sentimental value. The seller loves the way the home is decorated as well, so it comes across to them that I am attacking their decorating skills. And their "buyers' eyes" see the beauty of how their personal items add to the feeling of the home as a whole. The emotional attachment kicks in. It isn't easy at all.
What I can't seem to get across to the seller is that they are selling their little paradise. They are taking all their tchotchkes & photos with them to create a new home of beauty. A new owner will be taking over, bringing their idea of what home should represent. And looking at all the current seller's decorating is a distraction rather than a plus. The prospective buyer should be in the mindset of where they would put their own pictures, paintings & furniture, not caught up in accessories on the fireplace or the wall of photos on the stairs. The easier you make it for the prospective buyer to envision living in a home, the better chance there is of selling it.
BOTTOM LINE: Start packing it up. Your home has to be "show ready" anyway, why not have a jump start on the move. Make it a positive.