The Diavanzo are descendants of the Mioré. The Diavanzo are not an actual clan, but play a large part in the Mioré family lore.
The Diavanzo family are descendants of the Mioré. They were the small portion of the family that remained Zarosian after Zamorak took over in the 2nd age, but went into hiding because of the frequent attacks from the Zamorakian Mioré. In order to keep their identity on the down-low, they were forced to use a fake surname, and now have adapted to referring to themselves as members of the Diavanzo family since the 2nd age, and only the family royals even know of this long-lost secret.
The Mioré family were a band of Zarosian fighters and merchants that began worshipping Zamorak later on. After Zamorak stole Zaros's god powers in the late 2nd age, a small part of the family remained Zarosian, and they were referred to as "Zarosian Mioré" at the time. They didn't have an established home at the time, but they traveled in groups, not staying in one place for too long. They feared the Zamorakians would hunt them down, and they sure did try. They were really living on the edge in the 2nd age.
In the third age, the Zamorakians were becoming extremely violent and were coming up with sneakier ways of finding and ambushing the Zarosians, so the Zarosians had to take extreme measures in hiding themselves. During the God Wars, the Zarosians moved to the Kharidian Desert, Spread out in small camps. It was then that they adopted the name Diavanzo and were often straying from talks of religion, even with the family, as they were that paranoid. They didn't get much trouble from the Mioré, who were busy trying to win the God Wars for Zamorak. Ever so slowly did the family adapt to their desert surroundings and end their paranoia of the Mioré attacking.
By the end of the 3rd age the Diavanzo had no longer even thought of the Mioré, most wouldn't even recognize the name, besides the royals. Not even tall tales existed, and this is how the royals liked it. The family's camps began moving ever so closer together, and many settled in the town of Pollnivneach, although the family was still dotted around here and there. The family actually lived in peace for once, not being bothered by the Mioré, as they were off the map now. Their clever plotting in the 3rd age paid off, and they lived in peace, continuing to worship Zaros.
The 5th age continued like normal until the 164th year. An important document noting the location of the family was lost in a sandstorm, and eventually found its way into the hands of the Mioré by some miraculous means. The Mioré's chaotic side was brought out as they went to pick a fight with the Diavanzo. They were rich and better equipped, but little did the Mioré know, a large part of the family were trained in the Ancient Magicks, thanks to Ava Diavanzo. After a battle that wiped out almost the entirety of the Mioré family, the Diavanzo royals explained the family's history to them, and the family went in chaos, for fear that there were more Mioré out there coming to get them. There was an uproar in the family and hell broke loose. Over the next few years, the paranoia managed to calm down, and they now live as normal, praying for the few that died in the battle.