Complex sentence: His mother-in-law continued to support the rebellious Boniface of Castellane and his allies, but Louis IX persuaded her to return Forcalquier to Charles and relinquish her claims for a lump sum payment from Charles and a pension from Louis in November 1256.
Split into simpler sentences: His mother-in-law continued to support the rebellious Boniface of Castellane and his allies. The mediation of Louis IX led to a settlement with Beatrice of Savoy, who returned Forcalquier and relinquished her claims for a lump sum payment from Charles and a pension from Louis in November 1256.