You don't need featherfall, boots of Mystra from Arcane Tower in Underdark grant it, and it has no long/short rest cooldown attached to it and applies featherfall to the whole group. Speak with the Dead you get as a passive spell from reading Necromancy of Thay and passing the checks. There is a helm in Act 3 on Helsik's house 2nd floor in one of the chests that gives detect thoughts on top of +2 to attack rolls and initiative. Disguise Self you can get from the digital deluxe helm item. Longstrider you can get from Act 3 boots which grant Longstrider and Freedom of movement as passives.
BTW you can also apply longstrider to multiple targets at no resource cost. I haven't tested if adding Halsin/Jaheira to the party and then removing them from the party will also remove Longstrider from allies, I don't think so.
Last edited by Zenith; 01/09/23 10:36 PM.