Pianostaff 4-part writing and rests

[Peter Danemo]

Hello!

I'm a pretty unexperienced Lilypond user. I'm working on the layout of a 
small piece. It's basically a hymn written using a piano staff. If both 
voices have a rest on the first beat and start on the second beat I get 
two quarter note rests. I need it to be just one. I learned how to make a 
rest invisible, but that doesn't change the position for the remaining rest. 

Is there a easy way of doing this?

Furthermore, the piece ends with just 3 bars on the last line. But i fills 
upp the whole page anyway. Is there a way of getting the 3 bars to take up 
the same as the bars above? Making a 4th invisible bar!?

Best wishes!
/Peter