In my opinion, you have not provided enough information for any type of answer. For example, where are the piles to be driven? Next to or under the grade beam? What type of brackets are to be used? Does the grade beam bear on top of the brackets or are the brackets attached to the side of the grade beam? What is the load on the bracket and the pile pile and what is the size of the bearing plate under the concrete?
The pile spacing is a function of the bracket strength, the available pile capacity, and the load capacity of the grade beam. All need to be checked. The smallest spacing should be used.
Was the design prepared by a professional engineer? If not, get one who is familiar, no, make that "very experienced" with pile design and underpinning design. Familiar isn't good enough.