Unemployment is currently high in Crete and even Greeks are finding it tough to find permanent jobs.
Summer work is relatively [stress relatively] easy to obtain in tourism although I suspect that will be more difficult this year as prospects for the tourism in Crete are not as good as usual. Most jobs are with UK tour operators doing meet 'n greet and other tour rep jobs, bar work, waitressing/waitering etc., cleaning hotels and apartments [generally long hours, low pay], labouring, etc.
Winter work is scarce and mostly centred around the 3 months olive harvest where there's strong competition for jobs fro, mainly, eastern Europeans prepared to for long hours of hard graft for low pay.
Year round work is even harder to find unless you have particular skills that are in demand and jobs like those are unlikely to be open to foreigners who don't speak fluent Greek. Apart from that you may find work with an estate agent, especially with one of the many British owned ones, but the property market here is in much the same state as in the UK. Several developers have failed in the last couple of years and agencies have closed down or cut staff so prospects are not great.
There are many existing cleaning/property maintenance companies and they are competing fiercely for work and some have been forced to give up. Some are properly established firms operating legally but quite a few one man bands that may be operating "on the black". That option is not recommended because if the authorities catch illegal operations very heavy books tend to get thrown. Depending on the type of business it can take a lot of time and expense to set up legally.
What would you plan to do with your experience in retail? There's a handful of British owned shops selling foodstuffs but I doubt that you'll find many other opportunities without fluent Greek.
You also need to take account of Greek recruitment policies. Most businesses are small family concerns. Available work goes first to immediate family then, cousins, distant relatives, koumbaros [best man or godparents of one's children], other close friends, casual friends, friends of friends, anyone Cretan, anyone Greek, Greek speaking foreigners, others. OK, that's a bit tongue in cheek but there's a grain of truth to it.
Earnings are generally low. It's widely reported that average take-home is about €800/month and, in the present state of the Greek economy, many workers are threatened with salary reductions and loss of other benefits - what many of the current wave of strikes is all about and inflation is quite high [like the UK, higher than any official figures.].
I'd suggest that you think very carefully before committing yourselves unless you have sufficient financial resources to see you through a couple of years while you try to get established.