My parents inheritance is not going to be that much though. The 1.5M windfall will be divided among 8 kids (yeah I have lots of aunties and uncles) so my parents' share is about $187.5 K. Anyway...when the time comes...
I don't know what taxes are like North of the border, but it seems that no one has pointed out the fact that your grandmother's capital gains siutation may change this substantially, depending on what her net cost basis is...not to mention gift taxes.
In the US, you can gift away during your lifetime and use up your personal exemption (currently either $1.6 mil or $2.0 mil - I haven't been keeping track) to give away assets free of federal inheiritance/gift taxes, and not be stuck having to use it only when you die. If Canada has a similar inheiritance tax/gift allowance, then your grandmother would have to clearly indicate that when she cuts the check (not to mention fill out a few forms to send in to the gov't).
Also, it could be worthwile to pay a lawyer a small sum to possibly create an entity to buy the business from your grandmother for a certain amount, and then have the entity sell the real estate/businesses and disperse the proceeds...or, would a family member be intersted in buying the businesses and paying off the other family members using mortgages and lines of credit (depending on what the cash flow and net margins of the businesses are like)? If an entity were to purchase everything from grandma first, it could (but not necessarily) result in a much different tax bite than if she merely started cutting checks left and right.
At any rate, I highly doubt that your parents would be netting $187.5k if she sells everything for $3 mil, given that taxes of some form would be owed (and possibly a double-tax, if gift/inheiritance taxes rear their ugly head).