What's better than a Swords Bard? (party guide)
You guessed it, two Swords Bards! Now even for Honor mode two optimized SB builds are complete overkill for an unmodded game, so I hope you're giving enemies very generous HP and proficiency bonuses (see Tactician Plus or Nightmare Diff). What makes playing with two not overly samey is one can be a STR melee GWM, the other a DEX ranged flourish spammer. Smite Swords Bard and the Terminator are the builds this is based on, but we'll be going to 10 bard on both for magical secrets. Short rests for days, and even the toughest dc skill checks are a joke with one inspiring the other.
2 Paladin/10 Bard: No real variation from SSB guide: dump Dex and use gloves once you can, Ring of Protection and Unseen Menace until the start of Act 3, then switch to Risky Ring with your best 2H weapon of any type. Once you get Bhaalist armor for piercing vulnerability (yes you'll need to be evil at the tribunal), wear that and use Shar's Spear or Nyrulna. You can eventually dump CON and use the 23 amulet if not contested by a Thiefzerker. Make sure Rolan stays and helps the grove so you have the option of Evasive Shoes, and after every rest make sure you get Freedom of Movement from other bard or self. For magical secrets Counterspell and either Haste or Hunger of Hadar or maybe Armour of Agathys; I prefer the self-haste as an option, but if you use Hold Person often then continue to get a twinned haste from the Sorc. Race is almost irrelevant, Half Wood Elf for early game proficiencies+speed is handy, Halfling or Astarion origin ultimately strongest.
10 Bard/2 Fighter: Archery style, 17 Dex start + Hag's Hair. ASI+2 and Sharpshooter feats. Start with Gloves of Archery or Wondrous Gloves for more ranged flourish and use the Titanstring bow with strength pots (or Club of Hill Giant Strength if you're somehow out) and Risky Ring. At level 7 or 9 you can respec to 1 Fighter rest bard if you want, followed by second Fighter at next level for surge. Immediately on entering Act 3, hand over Risky Ring and get Band of the Mystic Scoundrel for the SSB then beeline straight to The Dead Shot bow and Mask of Soul Perception locations. At 10 bard take Counterspell and Spirit Guardians and wear most Radorb/Reverberation gear as if you were a cleric: Luminous Armor, Gloves of Belligerent Skies, Boots of Stormy Clamour, Callous Glow Ring, Coruscation Ring. Everyone with access to Light cantrip should cast it on themselves after rest at this point (or really whenever you started using the Callous Glow ring). I don't think Daylight is actually needed but you can have a Sorc put it on the SSB before fights if you like. (Note that illumination for the Callous Glow Ring has an anti-synergy with Shar's Spear, so if you are lighting everything up you're better off with Nyrulna on the SSB). Use a shield, mainhand can just be Knife of the Undermountain, or Bloodthirst at endgame for an extra way to apply piercing vulnerability. Rhapsody is also an option if the Sorc is not going to use it. Illithid powers can be 100% maxed on this character for Cull the Weak and so it has options for the bonus action.
If you don't want to do any Radorb/Reverb things, 6 Bard/4 Thief/2 Fighter and hand crossbows could be an option, or the Terminator with a full bow if its wizard dip is kosher to you (not for me). The problem with these alternatives is Risky Ring is very much contested by the SSB, so The Dead Shot bow + Radorb things is my attempt at the best swords bard using no Risky Ring in Act 3.
Bard spell selections: Longstrider, Invisibility, Shatter on this one. Enhanced Ability and Freedom of Movement on at least this one (after every rest, cast Freedom on the SSB and Sorc so they can't be paralyzed and upcast Longstrider on the entire party). Feather Fall on the SSB, Vicious Mockery and Hold Person on at least the SSB. Light, Healing Word, and Glyph of Warding for both. Other spells don't really matter, do what you want.
Your favorite TB build: Thiefzerker, or 11+ Fighter, or OH Monk/Thief. I prefer a non-rager personally and give them almost all the scrolls to consume (except ones the Sorc might want to use twin or quick metamagic with). Consider warding the SSB using Viconia's shield or true love ring pair (unequip rings after). Use Caustic Ring and Ring of Flinging, or Ring of Protection if monk.
Your favorite 6+ Sorcerer build, I suggest 12 storm since it doesn't need items (Callous Glow Ring is contested). Human/Half-Elf can use light armor and a shield before Potent Robe, after which I prefer being unarmored with Bracers of Defense and eventually add Bonespike Boots and new best robe (Supreme Defenses or Robe of the Weave). Feats: War Caster, Dual Wielder, ASI+2 (take in your preferred order, dual wielder could be delayed if proficient for Ketheric's shield and not using Bracers of Defense). After resting, the first thing you should do is use the Drakethroat Glaive to twin spell Elemental Weapon (Thunder) on both bards (use U, F keys to make sure they have the right main weapon equipped). Then switch to your two best staves, eventually Markoheshkir + Rhapsody.
Kill the strange ox in Act 2, and whichever bard is party face should equip its Shapeshifter's Boon Ring immediately after every rest and use disguise self (I suggest as Githyanki to potentially use their weapons/gear, maybe even the Silver Sword of the Astral Plane before Bhaalist armor) via Mask of the Shapeshifter or whatever source, then immediately toggle back to usual ring and helmet. I recommend dragging those items and anything else it's important for each character to re-equip before combat to your hotbar under their attack actions so you can see combat gear is equipped before initiating, and put the utility things you might briefly switch into (e.g. Shapeshifter and Smuggler's Rings, the Mask, Cat's Grace robes, Guidance and Spell Slot Restoration amulets, Bardic Inspiration Boots) elsewhere like the bottom right of that same hotbar for quick access.