There's no problem at all with selling the properties below their market value. (It's your property and you're free to do what you like with it).
However, if you die within 7 years, the tax man will treat each sale as if you sold the property for �110,000 and then gave �40,000 back as a gift. i.e. you'll have given a total of �80,000 in gifts.
You're allowed to make gifts of �3000 each year without this counting for tax purposes. Additionally, you can carry forward an unused allowance from the previous year. So, assuming that you you don't make any other gifts in the two relevant years, the tax man will disregard �6000 and treat the sale of the properties as including gifts, from you, of �74,000.
When the total value of your estate is calculated, all of the usual things will be added together and then an additional �74,000 will be added on top. Inheritance tax will then be charged at 40% on the amount by which the total value of the estate exceeds the threshold (which is currently �285.000). If the value of the estate was already above �285,000 before the gifts were added in, that would mean that the inheritance tax would rise by 40% of �74,000 (= �29,600).
Remember, though, that the starting figure for calculating your estate would start �220,000 lower, because you no longer owned the cottages, so things wouldn't be quite as bad as the previous paragraph might indicate.
Remember, as well, that those gifts of �74,000 only count if you die within 7 years. After that time, they're completely disregarded.
Chris