It sort of depends on what kind of Wizard JP wants to be. Wizards are divided into multiple playstyles which Wizards can play well (Although roles like (de)buffers are better handled by other classes like Sorcerer/Bard. Let's examine this a different way. There's a traditional metaphor for party composition, where there's 3 elements to a party - the Anvil, the Hammer, and the Arm
The Anvil is the one essentially controlling or impeding the enemy or reducing their capability so it makes the Hammer's and Arm's job easier to do - reducing/nullifying enemy speed or actions, removing them from the fight entirely, or altering the battlefield. Feats like Sentinel help fit this role, along with a slew of spells, class abilities and actions like grapple. It's also important for an Anvil to be high in initiative, to better set the encounter for the rest of the party.
The Hammer is pretty self-explanatory - do damage, or otherwise end the encounter.
The Arm's job is to make sure the Anvil/Hammer effectively do their job - buffing the hammer to do more damage/move better assist the Anvil if he needs help filling in a role. He's the enabler, and needs to be flexible to react to each situation.
So with those explanations out of the way, let's see what we have. Berg is obviously a full-on Hammer - that's not even a question. Ramus is another story - being a Light Cleric, he's an Arm with some tendencies of a Hammer with spells like Fireball and Scorching Ray, and taking War Caster (Right?). If JP ended up being a Wizard, he would do fine as the parties Anvil - Conjuration, Illusion, and Necromancy are fine schools for that, as yes, summoning (the dead) would increase your action economy, affect the enemies positioning, and whatever else summons do. Illusions can do a whole bunch of things, and really limited only by the player and what the GM allows. I don't think the group "needs" another hammer, but obviously taking spells for damage wouldn't be a mistake. Sorcerer does some things better (due to Metamagic), but the skillset of Wizards are probably better suited to the campaign. Lastly, taking the "Alert" feat would help.
With that, let's say JP does try to fill in the Anvil role. Well, that's 2 ranged characters, with Berg by his lonesome. I don't think another Rogue would be amiss. Specifically, one using the Swashbuckler archetype from SCAG, specifically for the "Rakish Audacity" ability, which removes the requirement that you need advantage if you don't have an ally that also threatens a creature to apply Sneak Attack. This gives the party a character that has a boatload of skills (6+Thieves tools assuming no overlap), and good options/positioning for combat as someone that can either help take some heat off of Berg, or a buffer between the two casters while still retaining damage.
...Boy this ended up being a lengthy post for something that probably won't happen.