Press i
Add a piano instrument
Click the first measure of the bass clef of the first piano
Shift click the last measure of the bass clef of the first piano
Copy (Ctrl+C)
Select the first rest of the second piano bass clef
Paste (Ctrl+V)
Press i and delete the Bass clef of the first piano and the treble clef of the second piano
select the brackets and press Del
Drag a bracket from the bracket palette, double click it and change the size
Comments
Press i
Add a piano instrument
Click the first measure of the bass clef of the first piano
Shift click the last measure of the bass clef of the first piano
Copy (Ctrl+C)
Select the first rest of the second piano bass clef
Paste (Ctrl+V)
Press i and delete the Bass clef of the first piano and the treble clef of the second piano
select the brackets and press Del
Drag a bracket from the bracket palette, double click it and change the size
This video can help: https://www.screenr.com/LW2s
If you need further help, it's better to use the forum http://musescore.org/en/forum
Thanks for your quick help