are fish oils good for everyone?.. I heard they are good for the heart and posssibly adhd?

Okay so I just ran out of my arbonne vitamins , they were very expensive and I took 5 different vitamins 2 times a day with those arbonne packs. I was told that the one a days and centrums ect dont give you all of what you need in one tablet. So I untill I get my old vitamins again I am taking my sister skin and nail vitamins its just one capsule, do they also help your health? Bad hearts run on the family so my bro told me to take fish oil vitamins daily for a healthy heart is that true? and it could help with adhd possibly is that true? However my aunt who is becomming a nurse said that they can be bad for you if you do not have a heart prob... is that true? I know I asked alot of questions can someone help please. Just tryong to find a good vitamin that will help with my over all diet untill I can afford to do the whole trader joe healthy diet and get back to my arbonne ones