Half dragon question

OK I'm new my friend will be dming he said anything goes as long as there is rules that allow my question is I wanna play a half silver dragon elf with a red dragon blood sorcerer background* silver dragon stays with mother who is also a sorc to keep the ancestory in check and under control* is this legal and if not what rules does it break ty in advance 

Well, you'll need to specify what system you are playing, but this sounds like the sort of thing that is more up to your GM than covered specifically by the rules. That said, I'd expect one of the mods to drop by in a bit with a reminder that the Roll20 forums are a very focused forum for the use of the Roll20 system itself, not for rules explanations for various systems. There are quite a few reddits and other forums available for those depending on your system.

(right on cue...) From the Roll20 Community Code of Conduct : The Roll20 Forums exist to discuss topics directly related to the use of the Roll20 program. Anything that more fittingly could be discussed on another website SHOULD be discussed there. Here are some good places to discuss this topic: /r/dnd /r/dndnext