Firearms seized. Is this legal?

It's called "exigent cirstances". If the police had probable cause to believe that you may use the gun(s) to harm yourself or someone else, then they have certain latitude that they normally would not have. It would be on them to prove this, but that would not be too hard to articulate due to the nature of the call. Also, they are not using these guns as evidence against you in criminal proceedings. Talk to an attorney if you wish, but I do not see the potential for a "gold mine" lawsuit here. You could sue to get your guns back, but that's about it. On the other hand, if they had knowingly or negligently left the guns there and you had killed yourself, then your family would have grounds for a lawsuit. Under the cirstances described, I would have done the exact same thing the officers did.