"Prenuptial agreements can bring validity into question when they center around disposition of assets in case of divorce. You can see by the canons above that marriage is permanent partnership. However, a prenuptial agreement with asset allocation in case of divorce brings in to question both Canon 1101-- the agreement is a positive act that excludes an essential property of marriage (permanence). Also, Canon 1102 specifically says marriage cannot be subject to future conditions."
"Each diocese has their own process, but during marriage prep you would be asked about any prenuptial agreement. If you have one, it would have to be investigated and could be an impediment to proceeding with the marriage. If it's based on divorce-- it's almost certainly invalidates consent. You would have to rescind such an agreement before being allowed to proceed with marriage."
"In the case of widows/widowers setting up inheritance rights for children of the first marriage upon death (NOT divorce) the church does not consider consent to have been compromised." forums.catholic.com
Can. 1101 §1. The internal consent of the mind is presumed to conform to the words and signs used in celebrating the marriage.
§2. If, however, either or both of the parties by a positive act of the will exclude marriage itself, some essential element of marriage, or some essential property of marriage, the party contracts invalidly.
Can. 1102 §1. A marriage subject to a condition about the future cannot be contracted validly.
§2. A marriage entered into subject to a condition about the past or the present is valid or not insofar as that which is subject to the condition exists or not.
§3. The condition mentioned in §2, however, cannot be placed licitly without the written permission of the local ordinary.