This all started with the American "Sub-prime" mortgage market. These are mortgages to riskier customers. Basically banks taking too much risk and thn turning around and finding that more people than they thought were defaulting. Consequently they were suddenly worth a lot less than they thought they were.
The banks don't know who's lost out by how much so they're very jittery about lending money to each other - hence Northern Rock.
Also the "sub-prime" market in the UK is affected. People can't get 100% mortgages any more and have to pay much more for higher percentage mortgages. This is damping down the UK housing market ( which as you have 3 mortgages will probably affect the value of your properties)
If the value of your properties falls too much compared to the equity you have in them, you may find it difficult when your 2 year deals run out. The mortgage lenders won't forget this quickly!
It really all depends on how much you owe compared to how much your assets are worth.