I've just put your ages, heights and weights into an online calculator. Assuming you're totally sedentary, Dean, you're looking at around 2600 calories a day to maintain your current weight. Lisa, you'd need around 2000 a day to maintain. Knock 500 a day off, and you'll lose a pound a week. (Well, you would in a perfect world in which our bodies obeyed the maths perfectly. It tends to be a little more complicated than that.) A pound a week is a very respectable amount to lose, and would have you both almost four stone lighter in a year's time, assuming you adjusted your calories downwards a little from time to time as you got smaller.
Obviously this doesn't mean you necessarily have to calorie-count strictly. Some people don't do it at all and still lose weight. But it does show that you really don't need to be, for example, only eating an apple for your lunch every day. You can eat proper meals and still lose weight, so long as you're making healthy choices.
Giving up after a few weeks - an awful lot of us here have been there, time and again. One of the major causes of giving up is feeling like you're too restricted and can never enjoy food again. That's why it's so important to make sustainable changes, that you can keep up for life. Another big problem a lot of us have is feeling like we're not losing fast enough, and so giving up because it doesn't seem worth it. You must have seen those magazine articles about people who've lost a hundred pounds in two months or whatever. Ignore them. Ignore all those adverts you see for miracle pills that will make you lose twenty pounds in a fortnight. What they don't tell you is their test subjects were very large to start with, and after that initial high loss they settled down to a couple of pounds a week loss. This is a marathon, not a sprint. But believe me, it's worth taking a long time over.
Am I right in thinking you're in the UK? You'd be very welcome to come join us in the UK Challenge Chat thread, or perhaps check out some of the challenges in Weight Loss Support. Might help you to stay motivated. Good luck!