For 24-70mm (35mm equivalent) F2.8 (not considering the difference in aperture for different sensor size yet).
Panasonic: 67.6 x 73.8 mm / 305g
Sony: 87.6 x 136 mm / 886g
The most compact one from Sony own lens line up should be the 28mm F2 d. It weights 200g but is around 7 cm in length. Won't call that a pancake Meanwhile, Panasonic 14mm F2.5 pancake lens is only 55g. Cannot compare at all
Oh yeah... Don't forget to let your dad know he's downgrading from APSC to M43 if it really happens. Later he wonder why the performance different
Granted, the optical quality of the cheaper FF lens are not as good as the Pro line on mFT, but some things have to give I guess. Just exploring an additional option.