One quick comment on the Seville orange,
There is not much published on the effect of the different preparation that you can make with those, but from a recent Japanese one, it seems that marmalade, which contains a lot of peel from the fruit, where furanocoumarin is present in higher concentration, has the same CYP3A4 inhibitory effect than the grapefruit juice.
http://www.ncbi.nlm.nih.gov/pubmed/21532264
So in conclusion, it is best to avoid British orange marmalade.
