The Income Offer Curve (which is the same as the Income Expansion Path) shows us the effect of a change in nominal money income on the consumption of both goods (in a 2 good model) in the real 2 good indifference curve space. Thus, to derive the income offer curve, one shifts the budget constraint by varying money income, and joins all the points of optimality. If both goods are normal goods, the income offer curve is upward sloping; if one of them is inferior, it is downward sloping.
The Engel Curves can be derived by looking at the Income Offer Curve. The Engel Curve shows the relationship between ONE particular good and money income in a graph i.e. in the X-I space. The Engel Curve for both goods can be figured out by looking at the Income Offer Curve.
So, in a 2 good model, the income offer curve summarises the effect of a change in money income on both goods.