Upgrade party of four?
 

On the regional flights out of HKG, have been lucky at getting upgraded (usually at checkin, sometimes at gate) myself (gold MP) + 1 (green MP) pretty regularly.

On this next trip, will need to fly myself +3. Wanted to take the grandparents along (no status). Has anyone had experiences with getting all four pax upgraded or should I just split my bookings?

I assume we're talking about opups here and not same-day mileage upgrades? If mileage, theoretically it's possible as long as there are enough unsold seats. If you're hoping for an opup x4 -- I'm sure one or two other FTers have probably hit the jackpot that way, but if it were me I would not be getting excited about the prospect of an opup in this circumstance, and instead would focus on getting excited about a trip with my family.

if you really want them to have a great experience of the premium cabin why not upgrade the grannies with your miles and hope for your op-ups since it wouldn't be so much of a disappointment when not given. ^

Less than 2 hour flight - really not worth the miles TBH. Will split up the reservations then and give them the op-up if I get it.