voltage sensing?

That would be a fairly complex circuit.

The first thing you would have to do is create a stable voltage reference, which can be done with a 7805 voltage regulator.

You would then have to scale the voltage you are trying to monitor - typically cutting it by 66% works well with a 5vdc reference.  This can easily be done with a voltage divider circuit.

For the limits you could use an op amp for each limit.  You would put your scaled voltage on one input, and the wiper of a pot on the other input.  The pot will be set to the limit.  For the upper limit you'll need to put the pot to the (+) input of the op amp and your scaled voltage ot the (-), for the lower limit you'll reverse it, put the wiper on the (-) and the scaled voltage on the (+).

You would then need to take the output of each op amp and run it to a 2 input  AND logic gate.  The output of the logic gate would need to go through a transistorized drive circuit and then can be connected to a relay.

A simpler approach would be to utilize a microcontroller.  You'll still need the voltage divider to scale the input voltage but all the limits can be handled in the software.  You would also still need the transistorized relay drive output.