Samui is a nice place to visit, but when living there it's very small, you drive around it in a couple of hours. A good chuck on the island is for tourists and not really suitable (imo) for living.
Samui is too small, you'll outgrow it very quickly. You'll be reliant on either flights or a ferry to travel elsewhere in Thailand, another added expense especially for a family of 3. A location on the mainland would give you more options, and you can still visit Samui if you still desire. Samui is obviously much more expensive than other potential locations.
If you're working in Thailand surely you would be on a Non B visa with the associated work permit and therefore the financial problems do not apply. However if you're working in contravention of your visa conditions then I would not be advertising it on a FB group.