they must be leaking fluid if they have gone soft check level in resivior under bonnet .
Its dangeous to drive !!! as you discribe dont go out untill you have found the problem hears the list of what it might be.
leaking brake pipe any of the metal pipes connecting the brakes or the rubber ones at the calipers.danger 10/10
leaking caliper thats the part at the discs or slave cylinders at rear drums they both have seals which can leak you can top up the level with brake fluid to got u to garage to get it fixed.danger 8/10
master cylinder is next to the tank that hold brake fluid under the bonnnet the seals also can go in this part and dont show any leaks danger 10/10
all brake problems are serious and need to be addresed as soon as posible think about the people you could injure or kill dont take chances with your brakes.
Tom Wilkinson, April 2013