To spend them, install Electrum on an air-gapped device and re-create the same wallet but use xpriv.
OP has now two keys, but the the problem is that the one that is shared with coinbase is encrypted and there is no way to import that to electrum.
In multisig coinbase wallet, there are 3 keys and they are as follows:
- An unencrypted key which is owned by the user and coinbase has no access to that.
- An unencrypted key which is owned by coinbase and the user has no access to that.
- An encrypted key which is owned by both coinbase and the user.