I've got the Accord estate and had a similar problem. Took ages but we managed to squeeze in two child seats either side and a booster seat in the middle. The two child seats were Maxi Cosi Axiss. It is tight but does the job, for now.
As said above we were looking at a new car but a couple of new child seats worked out cheaper and less hassle. The main frustration was the side bolster on the rear seats pushing the seats into the middle.