Seriously OP, its the last DM that was the problem.
Where you screwed up was agreeing to DM this same party without laying down some ground rules first.
If I was you?
Me (as You): Ok guys, I agree to DM those same PCs from the last campaign in place of your last DM. But I have conditions. Those conditions are:
1) You'll need to rebuild them, in front of me, using the point buy for stats, and average HP. Feats and all Player options are available.
2) You'll all get 1 (Very rare or less) and 1 (Uncommon or less) magic item of your choice, and I get to veto anything I dont like for something different.
3) Artificer, you can have 1 extra Rare item or lower (that you built in your downtime)
4) Wizard, you can select 3 spells per level, at every odd level after 1st for your spellbook (taking into account scrolls found on the journey).
5) Barbarian and Paladin you can both also have 2 potions of your choice from the DMG of Rare or less rarity.
Also, and on a positive note, Tashas options are available for your characters, (including custom lineages, and new feats and archetypes) and (while keeping to the general theme of the PCs) feel free to deviate from your precise build last time (taking a few levels in an appropriate class, a different arcehtype, or a new feat etc) during this rebuild.
They're my conditions. Accept them, or I am not DMing those PCs. That's my final position.
The above starts everyone off on a level keel, lets you familiarize yourself with the PCs (watching them get built, and having an input into their construction), undoes a ton of the past DMs 'monty haul/ overly permissive' mistakes, and establishes you as the DM and person of authority who has control over his game (unlike the last DM, who seems to have been a pushover).
You've also softened the blow by letting them rebuild with access to new options, which is pretty cool and sweetens the deal.
The last DM did not have control over his game. Dont make the same mistake. If they dont like it, they dont play those PCs.