Bitcoin transactions and addresses are public knowledge; there is no way to calculate a private key by looking at a transaction/address.
You'll need to find the private keys themselves, otherwise your coins will remain un-spendable.
Descriptors with a private key (or xprv) in it are equivalent to their version with the public key instead, apart from also conveying the private key information.
For what purpose?
The descriptor field only reports the descriptor itself (i.e., without private key material). The checksum field reports the checksum for your input. This is also explained in ...
Using this python library (I am the author)
>>> from cryptotools import PrivateKey
>>> prv = PrivateKey.from_wif('5KUkQNKHA9cVmhSyKuNmop7r83DN2fMhPtNUW843Q6JxqRddEVz')
If the key is too large
>>> PrivateKey.from_int(1 << 260)
it will ...