Powering up Nualia's party

[Acora]

I'm going to be running Rise of the Runelords soon for some friends who've, in general, never done any tabletop gaming. Two of our players (who will only be attending some of the sessions) have experience, but the other four (yes, it's a party of six) have absolutely no experience, at all.

The fact that my party will be six players is my reason for posting. I'm aware that RotRL is designed for four players, and whenever my two experienced players aren't attending, I'll be running the campaign essentially as-written. I would like to ensure that it maintains its difficulty when all six players are there.

While thinking about this, something caught my eye. Nualia's group is set up almost as a standard adventuring party, and it seemed to me that it would be fitting if, at some point, her party and the PCs would duke it out.

My question is, if I have six players during said combat, should Nualia's group also have six members? Obviously, this would require both Tsuto surviving the Glassworks and the addition of essentially a homebrew character, but I'm wondering two things. Would this unbalance the encounter too heavily against the PCs? After all, most of Nualia's party have at least four class levels, and the one who doesn't (Bruthasmus, I believe?) is still a CR3. Would the addition of the other two members make a TPK or something close likely?

If an additional member would simply serve to make the encounter more challenging, but not unbeatably difficult, my second question is this: What class should the sixth member of Nualia's band be? My own party consists of a Fighter, a Ranger, a Sorcerer, a Rogue, a Cleric, and a Druid (the latter two being the two that may not attend every session).

Any advice would be great.

[RuyanVe]

Greetings, fellow traveller.

Going to spoiler it, just in case:

Spoiler:

First, Nualia also has the goblins at her disposal and her sponsor sent her 2 yeth hounds. Also, there are other denizens in the dungeon.
If your party retreats and regroups after every level, by all means include more adversaries on the dungeon levels!
Second, keep in mind that the encounter(s) will be in a dungeon, so space is at a premium.
Third, the party of Nualia is encountered one-by-one (first Bruth, then Lyrie, then Orik, finally Nualia with yeth hound). Thereby, it should be relatively easy to tune difficulty.
As for the sixth member, I think I'd add her on the final level where Nualia (together with the hound). Have her tinker with something before the shadows and have her arrive 1-2 rounds after your group engages Nualia. As for class I'd go with a... bard.
See Tremin Kaylos in the NPC Codex in the PRD.

Ruyan.

[Kalshane]

Keep in mind that a 6-on-6 fight between characters of equal levels is considered a toss-up. There's a 50/50 shot of either side winning, and even the victors are likely to take losses.

In my campaign, also with 6 players (and all of them experienced with D&D 3.x if not Pathfinder) the only addition I made to the Nualia fight was adding Erylium (who had escaped them earlier) and re-calculated her stats to make sure they were right (certain things that are supposed to be pre-calculated aren't, some are that aren't and then her domain powers need to be added on top of that) and they had a tough time. If I hadn't been using Hero points, they likely would have lost one, if not more, party members in the fight. The Yeth Hound alone forced the burning of Hero Points to prevent half the party from running panicked off into the dungeon.

[tonyz]

In general, add more enemies rather than make existing enemies tougher (Nualia and her yeth hounds have the potential, all by themselves, to TPK the party given that some members are likely to fail their saves vs. fear and then Nualia can whale on the others.)

It would be relatively easy to add a couple of 2nd level fighters or rogues to the party. A skilled goblin? Another cleric of Lamashtu? A bard in dommed love with Nualia? A couple of backup thugs hired off the streets of Magnimar (maybe as comic relief)?

[The Shining Fool]

If you want to increase the difficulty a little bit while keeping tonyz (extremely good) advice in mind, you might check out Rules Zero: Underlings. It's essentially rules for tossing in minion strength characters, so you aren't increasing the DC by much, but you keep the PCs' action economy from drowning your BBEG.