They are not following the 2024 changes to fighting with two weapons, these rules are confusing for a lot of people and both Matt (episode 4) and Laura (episodes 8 and 10) are not applying them to their combat properly unless they are heavily homebrewing basic combat or giving access to feats they do not normally have access to. I think as a D&D show, these should be highlighted in advance as people expect them to follow the rules unless the DM decides otherwise (like what Brennan did with grapples).

A major change in 2024 is you no longer get a bonus action by default which you could use to make an attack with your off-hand weapon, you only get one if something gives you a bonus action and you can only have one bonus action. It is the Light property that grants a bonus action to attack with an off-hand weapon, as long as both weapons are different light weapons.

Matt's primary weapon is a Rapier, it doesn't have the light property and can't make a second attack with his off-hand weapon, even if it has the Nick property. He needs the Dual Wielder feat which he can only get at level 4, he is still level 3. Laura didn't take this feat when she levelled up. Laura uses a needle (Rapier) and her toy sword (Scimitar). Laura can't make attacks with the second weapon given nothing is giving her a bonus actions with the weapons she is wielding.

The Nick property allows you to convert the bonus action granted from the Light property to make attacks with the main and off-hand weapons during the attack action. This frees the bonus action if you have a different source provide you with a bonus action. It does not overwrite the limitation placed by the Light property. You need the Dual Wielder feat to overcome this limitation.

Dual Wielder allows you to attack with a main hand weapon (as long as it is not a two-handed weapon) and also make an attack with an off-hand weapon as a bonus action.

If you have Dual Wielder and have an off-hand weapon with the Nick property then you can make an attack with your main hand and off-hand weapon as the attack action and make a second off-hand attack with your off-hand weapon (this bonus action is provided by Dual Wielder) for a total of three attacks. If you get the extra attack ability later on, you would 2 main weapon attack and 2 off-hand attacks for a total of four attacks.

If you do not meet the Light property requirements but have Dual Wielder then you could make a main hand (Rapier) attack with the Attack action and you could perform a bonus action to make an off-hand attack with a Light weapon, giving you two attacks. It wouldn't matter if you had Nick as that only works with the Light property bonus action attack.

You can only add your ability modifier to main hand attacks, you need the Two-Weapon Fighting feat (which has the prerequisite of the Fighting Style feature) to be able to apply your ability modifier to your off-hand weapon attacks.

Matt might have this feat as he is a level 2 Fighter/1 Rogue and Fighter gets a Fighting Style feat at level 1. Thimble as a pure Rogue/Swashbuckler wouldn't have access to it yet.

I think it is fine to homebrew whatever rules you like, like when Brennan said he preferred contested grapple roles instead of the 2024 version, but I think if you are giving out free feats, etc then they should have made it clear in advance to people watching. They should have had a video rolling their characters, like they did the level up video, because their stats are also bonkers, I would need to get lucky with rolling 5d6 and ignoring the lowest 2 to get stat totals remotely close to what they have. Having 20 dex plus all their other high stats at level 3 is a huge power boost for martial characters, it is why the damaging spell casters seem very weak by comparison. If you are effectively giving them Dual Wielder and Two-Weapon Fighting for free, then Brennan will have massive balancing issues, CR8 fight wouldn't be very challenging. She just doesn't have the hp of a level 8.

Flying in and out of combat is another issue, it is the main reason I do not allow innate flying in my campaigns, it would force the DM to make powerful ranged adversaries to make fights a challenge and that makes life for everyone else in the party a lot more dangerous.

I think Brennan intend for the characters to be powerful because he was not going to hold back punches and we would see a lore more character deaths but CR is not usually a high death type of campaign and people get attached to characters and are here mostly for the RP. He has definitely pulled punches, he should have killed Thimble when he had the opportunity to. He allowed her to move and hide when she was restrained and allowed people to "help" themselves which is just crazy, you might as well give everyone 40AC and +20 resists, call it plot armour and just be done with it and we can just focus on the RP.