Every 4 seater sedan can actually take upto 8 people weight in general, considering heavy passengers and cargo weight all together. More important is weight is equally distributed on front and rear axle for load sharing, if you load heavy objects only at back, then im sure something may go wrong.
About the bushes, what mechanic is saying must be right as bushes are seen by eyes and if you feel any squeaking on suspension or turnings that means its too late to change. Visual inspection is good enough in that scenario.