I've borrowed money from family and it can be sticky depending on the situation.

Make sure to be as clear as possible of the risks and be clear to yourself first and to them when will you cut your loses if things go south.

Otherwise, try to be as explicit as possible regarding terms and your plan. Usually family gives money based on relationship, not contracts and business/financial benefit and as such what is broken if things go sour is not a contract or cutting a bad business deal but relationships. So, watch for that.