It means that some problems are easier to solve if two people, rather than just one, think about the solution.
it mean no matter how much you dream, always stay grounded. like if your heads in the clouds and your dreaming about something always stick to reality
2 heads are better than one
It means that he is immature and that you can do better- alot better.
Re-write as: 'The problem, is that he is always arriving late to meetings'
make something bigger then what it is
When you are a global power it doesn't mean you are always right.
Yes. There is no word that cannot begin an English sentence. But that does not mean that it is always a good way to begin one.
probably
Yes, the word polycephaly does mean many heads in the Greek language.
to be interesting or attractive that people turn their heads to look...
How could we/they/you use it in a more practical/efficient way?
If you mean what I think you mean, it would be better to say, "Eva and you are going in identical costumes."