I would definitely go with Weight Watchers or Slimming World, as the best option here. How overweight are you both? Is it a health risk?
I ask because I knew of a couple of people who used Slimming World for free, as part of an NHS scheme, or something. It may be worth having a word with your GP to see if you could access these services at a reduced cost or for free.
Failing that, I can highly recommend a free app called My Fitness Pal
http://www.myfitnesspal.com/
You put in some basic info, height/weight etc, and chose how many calories you want to consume each day, depending on how much weight you want to lose.
Don't go mad and chose only a small amount of calories as it won't be sustainable and you won't stick to it. 1200 is about right (again, check with your height and weight).
You then add into your food diary each day, and it will tell you how many calories you've had and how many you've got left.
It's a really good way of keeping check of things.