[@Puppy0] Yeah you can do that. Side note, is that Aegon's kids are also dragon riders, and we'd have to come up with a valid reason for Jon and Dany to let a Paramount house have control of their own dragons. Right now, the only other house allowed to have dragons is House Velaryon (who have always been close to the Targs and are the only other Westerosi house to have dragonriders historically). So Aegon could just be a Paramour of Arianne's as well. It depends on what you want to do. 

I would advise having another character be the heir to Dorne, someone you designed to be the heir. If you consider the Sand Snakes and Doran's cousin(s?), House Martell is actually pretty big. Nymeria is just one of many Martell heirs. Viserys is the Prince of Summerhall and the heir to Dorne has to carry the Martell name, so it might cause some awkwardness if one of those titles doesn't go to an heir with the right name. Plus Nymeria isn't really heir material haha.