Hey!
You should research a bit (DJ and forum threads), there are plenty of good, more detailed, information and discussions about this subject. Basically, if you die of old age and have an heir they will inherit your belongings and titles and you will be able to play with them in your next life. Your successor can be an open NPC from your bloodline or an NPC you have a code for.
Again, a quick wiki/forum/DJ search will provide you more than that regarding family, death, contracts, etc. You can also find good videos about it on YouTube. Take a look =)