Actually Masha, to be painfully technical, the OP stated they "could be exercised for a minimum of 30 mins every day."
When a person states a minimum, and not a maximum, most ppl tend to then consider the situation from the mimimum given.
Sweetboy, all those points are very valid IMO. It's not just about exercising, it is about the daily needs of each dog, not to mention their socialisation and training requirements.
OP, I'm with the others, I would seriously consider looking at few older dogs that need new homes.