Craig Watkins can not force Ivy to buy the other house but since the other house is bigger than the first one, Ivy can also not take a legal action against Craig.
Explanation:
The house that was offered first by Craig Watkins for sale was canceled and he decided to back out from the deal. But since there was fear of a legal action by Ivy, he decided to offer another house to Ivy. But the other house that was offered did not fulfill the agreement and the requirements of the buyer.
But still he can not take any legal action against the seller because the new house that has been offered is comparatively a bigger one and has more value than the previous house. So this avoids the fear of any legal action. But still the seller can not force the buyer, Ivy to buy this new house and continue with the deal.