Hello dear Bitcoiners!

I have questions for the multisig experts and hope that somebody can help me:

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1. Lets suppose we have 5 keys (A, B, C, D, E). Is it possible to create a multisig address with the following payout structure: A and B have to sign plus one of the others (C, D, E). So something like a 3 of 5 but with the limitation that A and B must be part of the singning process? If this is possible, is there a name for this kind of multisig? Does anybody know where to find more information about this?
2. I heard that it is possible to create a multisig address where the numer of needed keys decays over time. Eg a 5 of 5 where every year one key less is needed. Does anybody know where to find more information about this?

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Thank you!