You just need to tell your wife where is located your encrypted seed, then she will be able to access your encrypted seed but not being able to decrypt it while your relatives will be able to access your password (if they unseal the envelope at least) but not being able to locate your encrypted seed.
You are just trusting two people instead of one. If you don't want to trust anyone, then trustless solutions are better.
AFAIK you can't spend anymore funds included in a timelocked transaction before its expiry date once your timelocked transaction has been mined.
You can spend the coins any time you like. The timelocked transaction can only be mined after the timelock has passed. If you need to spend the funds, then you can do so and then simply replace the timelocked transaction.
In addition, it implies to know at which date you will die. That's not convenient at all.
Not at all. Create the transaction for 6 months in the future. If you are still alive, invalidate it and create a new one another 6 months in the future.
You can check the service from time to time before losing your memory or dying, if you are afraid of that.
Maybe it's just me, but it seems absolutely crazy to me that you wouldn't trust your own wife to even know that you own bitcoin, but you are quite happy to trust a bunch of complete strangers (with a track record of terrible security and privacy) to store part of your back ups.