Descent (noun) refers to your origins such a family or nationality. I am of Maltese descent. I am descended from a British family. Succession is when you inherit something. When the Queen of Britain died, the succession saw her son Charles succeed her.

Succession means 'following on from'; it can refer to anything. 'A succession of events' is a sequence of events. People can follow each other in succession. Descent implies that the thing following something is related to [descended from] what was before it. It typically refers to people, but could apply to animals, plants, or other living things, or something that evolves [develops through adaptation] eg. language.