If you are refering to the sub frame under the engine then I had the dis pleasure of changing mine. Some of them were recalled for a weak weld on the lower a-arm and mine was not caught. To your question, if the bolts are the ones that bolt the sub frame to the body of the car then yes you should support the engine. I used a engine sling that rested of the inside of the fender wells and front beam above the radiator. this allowed me to place the car on a lift which made it alot easier to install. The engines weight rests on this frame and you might get away with changing one at a time but if they are have loosened on you they it would be better to be safe in case one of the others is not holding like it should be.