So I did some doubles pokebank OU testing, and so far i'm finding that porygon there behaves much like he does in singles with protect as the third move, working well with both electric and ghost conversions, benefiting a lot from support moves like stealth rocks, aurora veil, sticky web. The only big difference is that blizzard is preferable to ice beam. I Note that porygon Z does not work well at all in trick room though.
As for using discharge in electric porygons, you really need teammates that won't take damage and can attack while you use discharge, because being a multi hit attack it doesn't do as much damage individually as the regular thunderbolt, and the damage you can do to your teammates in both hp and paralysis status is as impressive as it is embarrassing. So no discharge for you if you plan on having porygon 2 as a bash brother.
As for porygon 2 sets that go well with porygon z in doubles,you could go with something like
Psychic/tri attack
ice wind/toxic
recover
psych up/trick room
psychic is there to deal with porygon 2's biggest threats, which are fighting types and toxic users, and is strong enough after getting boosted by psychic field, but tri-attack is also a solid choice due to to STAB and the status effects it can induce.
Ice wind is there for support; it's good to deal chip damage, but being able to slow down both foes is just good enough to give Porygon Z the opportunity to set up with z conversion, or for other strong attackers to be able to make the first move. If you have a teammate with sticky web you can use toxic instead though.
Recover is obvious, and psych up is good to take advantage of Z-Conversion stat boosts and eviolite at the same time, but it's also good be able to fight back dangerous stat boosters like zygarde, oricorio's dance etc. However being able to cancel a trick room on comand, or set up a trick room if you have a team for it can also be immensely useful.
