As said it depends entirely on your personal circumstances, eg are you working or inactive, and how long have you been here. You say 'earn' which suggests you are maybe a part time employee on a low wage or running a business that isn't doing very well, in which case you might be eligible for certain reductions and benefits. If you are, these are normally triggered automatically when your tax form is processed, so you may find that your taxe d'habitation bill is reduced and you may receive forms in the post telling you about things you might be eligible for, and how to apply. You might also be eligible for free healthcare, CMU-C - ask at CPAM. But if you really are trying to survive on that level of income I would suggest you see the assistante sociale and ask about things like food parcels and cheap electricity, because frankly I don't see how a couple can possibly live on that, it sounds like a desperate situation and I think you will need a stronger safety net than the state will provide.
Hi again Steve, I just saw your other post so I now realise that most of what I said above wasn't relevant.
Unfortunately the French social security system is struggling to cope with 10 per cent unemployment among the French. The pot is getting empty and apparently the only way Hollande can think of to keep it topped up is by increasing taxation on those who are working or running a business or have unearned income. Taxation is already sky high and right now France needs more people to come here and put money into the economy, not more people to come here and take money out. It isn't realistic to expect to arrive new in France and get help from the state, you need to be sure before you arrive that you will be able to pay your way. You will discover that France is like that - many things that one would like to do are not possible, so you have to start off by finding out what options are possible, and then choose from those. If you start off by deciding what you are going to do and then looking for a way to do it, you are likely to discover that there is no way.
If you want to live in France you need to pay into the system, therefore you either need a lot of money in the bank, or you need to find a job or run a business. I suggest you set up your AE businesses as soon as you get off the boat and you both work your fingers to the bone to try to make a living. Don't burn your bridges, make sure that you have an escape route back to Ireland because France is not a soft option and you wouldn't be the first nor the last that needed an escape route if things don't work out. Bon courage.