mmh...so I start again ToEE, this time (incredible) with a Lawful Neutral party of 8 character. Only a question: to save Paida and Prince Tormel, you need a free NPC's slot? Not that Scather interests me (no CB, NB or CN PC to use it) but Paida is quite useful both for Walden and Desperate Housewives quest
Yes. It is recommended to have always a free slot. You'll need it for others characters. And to summon in-game familiar you need a free slot too.
That is not actually true, you can use an 8 man party of wizards and sorcerers, each with thier own familiar if you so wanted, but it's always a good plan to leave at least one slot open for an NPC to join your group, though not absolutely neccesary.