I am a student and I do not have an inheritance to give yet, but that does not prevent me from giving my opinion. 
I am leaning towards plan A, but I think that a few elements should be added to make it even more solid. The idea of building a multi-signature wallet is really good for ensuring security, but it would also be important to train the heirs so that they know how to manage these assets. In addition, having clear documentation on the steps to follow and the locations of the backups could really help avoid confusion. For example, we can establish a document that explains how to access the backups and how to use the keys to recover the wallet, while showing them how to do it step by step. This would ensure that, even if something happens, the heirs can easily access all of this. Basically, plan A is solid, but good communication and preparation of the heirs are essential for a successful transition.
I am leaning towards plan A, but I think that a few elements should be added to make it even more solid. The idea of building a multi-signature wallet is really good for ensuring security, but it would also be important to train the heirs so that they know how to manage these assets. In addition, having clear documentation on the steps to follow and the locations of the backups could really help avoid confusion. For example, we can establish a document that explains how to access the backups and how to use the keys to recover the wallet, while showing them how to do it step by step. This would ensure that, even if something happens, the heirs can easily access all of this. Basically, plan A is solid, but good communication and preparation of the heirs are essential for a successful transition.
I appreciate you taking the time to comment on the subject, but I 've already made these comments myself in the OP.
4. Hold A1 yourself and give B1 to your inheritors. A2 and B2 will be stored in very safe places that you will determine. A1 and A2 will be known to you only. B2 will be known to the inheritors. So they will know where B1 and B2 backups are.
5. In your will, you will give them the locations of A1, A2 and specific instructions on how to recover the wallet using one of the A1, A2 and one of the B1, B2. Obviously you can let them know about your plan and teach them what they will need to do beforehand. So in your will you need to specify the locations only. But a recovery plan written in the will is not redundant in my opinion.
5. In your will, you will give them the locations of A1, A2 and specific instructions on how to recover the wallet using one of the A1, A2 and one of the B1, B2. Obviously you can let them know about your plan and teach them what they will need to do beforehand. So in your will you need to specify the locations only. But a recovery plan written in the will is not redundant in my opinion.