Is it possible to make a multisig address with 4 keys (A, B, C, D) that requires 2 signatures to broadcast a transaction, but one of the signatures MUST be from A?
With your question, I believe the person A is an important co-signer for that Bitcoin treasury. You want to add a condition that without person A confirmation through his signature, no Bitcoin transaction will be moved out of that treasury.
It is good to control that treasury but it has disadvantage and risk too. Like if that important co-signer passes away, bitcoins in that wallet will not be accessed. It's very risky.
The main reason we have multisig wallet is to avoid hacks, increase security and safety for our bitcoin, but it is not used to increase risk of losing our bitcoins.
If you want risk, you can set a 3/4 cosigner wallet with 4 cosigners: 2 from person A, 1 from person B, 1 from person C. Because that multisig wallet need 3 cosigners to sign a transaction, if only two people B and C sign a transaction, it will not be enough without a signature from person A.