What is the polite way to say a grandparent has passed away?
The common polite terms for 「死了」(died):


過身 (passed away)
去世 (left this world)
逝世 (departed from this world)
仙逝 (departed to the spiritual world)
走了 (had gone)


Example sentences:


他過身了
他已經去世了
曹操在 220 AD 逝世
我祖父早已仙逝
我父母都走了


走咗(走了) is the most popular one among Cantonese speakers  because of the vagueness ( as if the dead person was just gone for a trip) 


  What is the polite way to say a grandparent has passed away?


"祖父過身了" 


  could you provide the jyutping?


90% of the time Cantonese would use the two below:

我祖父過咗身 ngo5 zou2 fu6 gwo3 zo2 san1

我祖父走咗嘞 ngo5 zou2 fu6 zau2 zo2 lak6