A lot of writing on the Internet will propose OPOL (One-parent, one-language) as the best strategy for raising bilingual children. I’ve written here before about why I believe this is not the case (although it can work in some situations) and now there is research backing up the limitations of this approach. Follow the link to read the article on The Conversation.
on raising bilingual children 
The most successful multilingual family I know has children that speak 4 languages and they don’t mix them up. The speak one language for each room of the home, so the children’s mind has the languages separated because each was only learned in one of the rooms. The children all speak English, Finnish, French, and German.