8 party members mod does not exist, atm,
as the maximum of 6 "real" party members is hardcoded.
However it is rather easy to add RPCs of your preference to the game in your own mod:
get madgods Cosmic Forge Editor here
install and run Cosmic Forge, select the NPC editor, in it select any NPC,
select to "Create New ..." and select the RPC which fits best to min the required changes.
Adjust all parameters on both tabs for RPC parameters and spells.
Now the character requires an NPC script so he can be talked to and hired,
and an RPC script to work in party.
For an otherwise unmodded Wiz8, the fastest way to get an NPC script out of the game archives so that you can work on it,
is to open the desired NPC with NPC Editor, go to NPC script tab,
there select any script block, e.g. 0,
then "Add Quote", instantly delete the new quote, and save the script file(its located in \data\npc scripts),
now adjust at least the quotes in block 0, 1, 12 and 13 to fit to your character whe nyou hire him.
Repeat for 2nd desired PC.
Similar for the 2 characters RPC scripts.
Speechsets for those new NPCs:
You can use the existing speechsets to save much effort, 1st select "miscellaneous" in CF main menu,
navigate to \wiz8Installdir\data\sound and select to open the file sound.slf,
extract the folders "NPCS" and "PCS", they contain all NPC respectively RPC and PC sound files.
The sound set you like to have must be renamed appropriately to be recoggnized by the game,
the naming convention should be rather clear if you look at the files for an existing RPC,
basically the script file name in NPC editor "general parameters" tab is the base file name,
with either "NPC_" respectively "RPC_" in front of it and the related script block ID added at the end.
This has the advantage that you can still park your 2 artificial PCs and do any quest which require to recruit someone,
last not least the free choice of race and portrait without the need to read an even longer explanation for that,
than the wall of text above ;)
If you want to use an existing PC speech set, you have to copy the lines one by one from:
CF main menu -> String Editors -> PC Quotes Editor < desired characterand paste them into the RPC script,
this is probably the most time consuming part of the whole.
(to rename all .mp3 files in one go, you can use e.g. the free program IfanView -> "batch conversion/rename")
Thanks! I will try this out sometime, been meaning to experiment with the Cosmic Forge anyway.