Hi,

If you use 2 series you can have a separate trendline based on each series.

You can place chartobjects on a chart sheet. Start with a blank chart
sheet, to create this just make sure the active cell is empty with no
data in surrounding cells. Then press F11. This will give you an empty
chartsheet. Create the 2 charts on a worksheet and then change the
location to that of an object on the empty chart sheet.
Once the 2 chartobjects are on the sheet you can position as required.

Cheers
Andy