Applying a hover effect to all divs inside a well can be done using the following code:
.well:hover div {
background-color:green
}
However, if you only want to apply the hover effect to specific divs inside the well, you can specify them in this way:
.well:hover .div1, .div2, .div9 {}
If you tried something similar and it didn't work, make sure to use the correct syntax. This is how you can achieve the desired outcome.