Can we go inside the sun and come back?Forget going inside the sun. We can't even go within 4.8 million Km of the Sun. Due to the high intensity of cosmic rays and heat from the sun, you cannot simply make it past this point.
Now let us assume you have a spacecraft built for this purpose. It is backed up with a really strong case made of carbon heat shield. As you cross the 4.8 million Km mark, the integrity of the case starts to deteriorate. The ship wouldn't make it within 2 million Km of the Sun, although it could move past our initial restriction.
The surface of the sun is at 5500°C whilst its center reaches a temperature of around 15 million °C. No organism can survive these kind of temperatures.
Although speaking in a hypothetical scenario, you might be able to go into the sun. But I'm not sure about the coming back part.