Following my post The House of Bourbon Two Sicilies further research on the Internet led me to the online article House of Bourbon-Two Sicilies
This has very useful information on the dynasty and their marriages and children. It also outlines the two lines of claimants to headship of the House, and thus to the crown of the Two Sicilies, since 1960.
It also gives links to the official websites of both claimants.
That of the Duke of Calabria and his line can be seen at www.borbone-due-sicilie.org/
That of the Duke of Castro and his line can be seen at www.realcasadiborbone.it/en/
I do not feel qualified (at present anyway) to pronounce on the respective validity of the claims, and in the interests of equity and fairness commend both to readers.
The dispute between the two branches of the House is not clarified by the fact that both are currently headed by a Bourbon (Borbon/Borbone) who would claim to be the de jure King Carlo I.
The blog Royal Musings had this illustrated report of signs of rerconciliation between the two branches and a detailed account of the 1900 marriage and Act of Cannes that lies behind the split which happened in 1960 and can be read at RECONCILIATION IN THE HOUSE OF BOURBON-TWO SICILIES