Questions about pet parakeets – My brothers pets & he doesnt take care of them so I have to & Idk how?

My little brother has two pet parakeets that he has had for a few years. Well, he doesnt take proper care of them so I have to in order to keep them living. I change their seed, water, cage etc. but I honestly dont know if they need anything else, different seed, do their toenails need clipped? They are really long & curling under, is that normal? Is regular seed for parakeets ok? Should they be eating something else? Any info on these birds will be helpful, thanks!
- Creamsicle