London Elite is right.
3 award tickets, aiming for a premium class, during peak time to a prime destination is a hard ask. Not impossible but also not easy so one has to be realistic, Upgradable fares often require certain higher fare groups for it even to be plausible and then with certain programs there has to be a type of award space open for the upgrade to be possible.You run the risk of spending more and not getting the upgrade. And there can be upgrade copays that run you even more money.
You may do better just paying for a premium economy ticket and using points to offset the costs. Just make sure it's an actual PE product and not just an extra legroom situation.