Well, the amber conversion should be easy enough. Northen Brewer says their amber extract is a mix of pale malt and Crystal 60, up to about 10L. If you have brewing software, you can tinker with the mix until you get the right color.
As for that other extract, I've never heard of Mahogany Coast English, but I'm assuming Mahogany Coast is a brand name and it's just English malt extract. If that's the case, id just use Maris Otter.
It's too bad it doesn't say what kind of extract the English stuff is becase whether it's liquid or dry will affect the conversion. But the numbers are 1 pound grain = .75 pounds LME = .6 pounds DME. Cheers!