how can you just cast certain spells on the mages and spells on the melee's? cast them one at a time or can you cast one spell on certain people in your group, or just cast it on everyone in the party, and if so what commands should i use?
When you get in the party you have to ask the melee and range to get some decent distance between them, then you run up past the melee, sing a couple songs, then run back to the range, sing a couple songs. Each instrument has a range that you can use to make sure you get the right songs on the right people. Harps have a little longer range than wind instruments. After a while you can just sort of judge the distances and do all sorts of random things. In a perfect situation with a lot of room I'd do something like this: run up and sing Madrigal and Minuet on the front lines, then run away to single out the tank and put two Minnes on him, then run back and put a ballad on the mages, then run to each side and boost mind and intelligence for each respective mage. Most of the time this isn't possible, but in theory you could have two different songs on each member of the party if the spacing was perfect. You can't really do this though, so two on the mages and two on the frontline is usually standard.
also i notice the instruments have certain effects on songs, so i take it i can keep all the instruments and make a macro which equips the required instrument before playing the song that needs it.
Yeah, this is correct. I have a +3 charisma horn, but from testing it seems like the +1 Minne/Minuet/whatever instruments help a lot more than the charisma bonus. I carry around all my instruments and the macros look something like this:
/equip range Gemshorn
/p Buffing something.
/ma "Knight's Minne" <me>