Your multisig backup seeds are what gives you access to your wallet, wether you lost the device or not, the other security measures you take such as using pin to lock your wallet in other for someone not to have access to it is only effective on the device you're using, once your back up seeds are exposed your bitcoin is gone, they don't need to know your pin, your bitcoin is on the blockchain and not on the wallet used, what gives them access to your bitcoin is the possession of the keys to unlock the lock coins on the blockchain, not your keys not your coins.
Not third parties but cosigners, that's why it's a multisig bitcoin wallet, if you choose to allow for that.
Refer to all the above suggestions already given including their links to learn more.