Quite a few of them share platforms
Toyota Camry and Lexus ES
Toyota FJ Cruiser and Lexus GX
Toyota Land Cruiser and Lexus LX
Nissan 350/370 and Infiniti G Series
Nissan 350 and Infiniti M Series
Nissan 370 and Infiniti FX
only two cars sold by lexus (cars, not trucks) use standard toyota chassies. the other four (the GS midsize sedan, the IS compact sedan, the LS full size sedan and the CT compact sport hatch) are dedicated luxury platforms, with three of them being RWD.
infiniti, meanwhile, produces exclusively RWD cars (again, cars, not trucks) that, while based on japanese nissans, are exclusively infinitis in america and europe.
acura, meanwhile, has no dedicated chassis. all of it's cars are direct rebodies of standard hondas (the TSX is a euro accord, the TL is a standard accord, etc.)
this is why lexus and infiniti are dedicated luxury brands, like cadillac or BMW, while acura is a semi-luxury brand, like buick and lincoln.