Converting 45 byte shared key in pynacl to 32 byte key to use along with AES-CBC with 25 byte IV

Question

I am currently working on pynacl library. The problem is I need to use the 45 byte shared key generated to be used to decrypt an AES-CBC encryption with an 25 byte IV. But the AES-CBC can only take 16/24/32 byte keys and 16 byte IV. Can anyone give me some suggestions on how to convert the 45 byte key to 32 bytes and the 25 byte IV to 16 bytes size.