Ahh one of those "We're mad and we don't have anyone to be angry with." style lawsuits. Pretty much the Hail Mary from a lawyer who is getting their name in the paper but knows it won't go anywhere.
"Easy to remove gun lock" that has been tried multiple times and usually fails. "Gun lock" doesn't seem to be related to assault weapons and large capacity magazine but who knows what they mean, even when a gun is "Easily modifiable" it's usually not treated as illegal, because someone has to actually make those modifications. The same will probably be the case for the kevlar. (at the time of the shooting it was legal).
Youtube contributing to radicalization is a laugh, it's an attempt to get their name in the papers and will be dismissed easily. They'd have better chance to name the channels that radicalized him, but first amendment rights would be near absolute here. Besides which "Radicalization" isn't the same as a conspiracy or orders. It's the difference between someone riling up the crowd until they're in a fervor which ends up in a riot, and someone specifically telling people how to riot and who to target. (Even if can be tried as crimes, one is a conspiracy, one is not, and even that "radicalization" would be neither.) Even "I wish someone would go shoot up ..." would be hyperbole, and thrown out as well. It's pretty hard to break the first amendment protections in America (And that's a good thing, if you think it's not imagine if the other party is in power and wants to squash your speech... yeah let's keep that amendment in place).
The same will be the case against Facebook for all the same reasons.
If you think Google should be responsible, then you think the park that someone is radicalized in should be responsible for what's said in it, or the email provider is responsible for every single piece of mail that is sent on it, even though it might not have access to see that mail... it's a silly idea even assuming they could even do that. Maybe they're hoping to scare Google to change it's algorithm, but I doubt that will happen either.
The case against the parents is another one that people try and again... unless there's more than their saying, you still can't sue someone for being a bad parent. Hell there's a better case against the parents of Ethan Crumbley, and even that cases is still pretty shaky, and involved the parents actively ignoring every warning sign, and buying the kid the gun. This there's nothing that seems to be pinnable on the parents.
You know it sucks and I know there's a lot of hurt people but lawsuits like this ultimately fail because it's like rolling the dice, but history pretty much shows this is hoping for a one in a million chance that they get lucky, and they won't, because it's one in a million, and then they'd have to hope it's not overturned even if they do win.