Tax Credit / Working Tax Credit question

Hi,
Both my husband and I work over 20-hours a week in our respective new businesses. We have an 18-month-old son and are receiving Working Tax and Child Tax Credits because of our low income. Currently, my husband takes £1,000 per month from his business and I earn an average of £350 per month from mine. I’m a sole trader and my husband is the sole shareholder and Director in a Limited Company.
Our Tax Credit award for the 2017/18 financial year is just short of £6,000 and the money is needed month to month to keep our heads above water. However, my husband’s business is seasonal (winter) and showing promise now that industry traction has been achieved. We are confident that by early 2018 he will have built up a pot that would allow him to increase his monthly take and/or draw down a decent dividend.
Assuming we can pull a decent dividend, it would put our earnings for the entire 2017/18 year above the threshold for receiving Tax Credit assistance. My question is what will happen at the end of this financial year once all the numbers are cooked? Will we be hit with a bill for nearly £6k to pay back all the money that we desperately need right now? If so, what is the time frame/payment plan for paying that money back? Has anyone else had experience of this?