How can Jesus come and fulfill the law and redeem everyone, but Jews remain in a Covenant with God?

They haven't. Assuming that you believe them to be descendants of those old Jews who rejected Christ, then they are branches who have fallen off the tree. We should pray for them to come to the faith and be grafted back on again.

If instead you consider the vast majority of them to be following an essentially new tradition (babylonean talmudism), given its new emphasis on matrilineal rather than paternal descent, its vast quantities of new text and beliefs, and lack of similarity with the old ways, then they are just pagans whom we should pray for: for them to reject their old ways and come to the faith, that they might be grafted onto the tree.

We're not american dispensationalists, catholic doctrine is more 'fulfillment/supercessionist'.

How can Jesus come and fulfill the law and redeem everyone, but Jews remain in a Covenant with God?

They haven't. Assuming that you believe them to be descendants of those who old Jews, then they are branches who have fallen off the tree. We should pray for them to come to the faith and be grafted back on again.

If instead you consider the vast majority of them to be following an essentially new tradition (babylonean talmudism), given its new emphasis on matrilineal rather than paternal descent, its vast quantities of new text and beliefs, and lack of similarity with the old ways, then they are just pagans whom we should pray for: for them to reject their old ways and come to the faith, that they might be grafted onto the tree.

We're not american dispensationalists, catholic doctrine is more 'fulfillment/supercessionist'.