You will have to support it after the consultants move on anyway. If you assume the consultants know what they're doing, and do not take active ownership of the work product, you will never get the result you want. This is not due to the consultants' malfeasance or dishonesty, but rather the opposite. The consultants' job is to complete the assigned tasks as well as possible, on time and on budget, per your stated requirements. Language and documents have their limits.
Reality has a nasty way of being different from the concept.
Your task is to ensure that your original goals are being met and to manage changes to the project as those goals confront the emerging reality. If your people are too distant from the process, they will not be able to effectively understand or respond to the issues that arise. Don't be intimidated by lack of knowledge. Due to the fact that the consultant has expertise your organization lacks, you may find yourself in the position of having to make budget, design, and functionality decisions in areas in which you and your organization have no expertise. This is possibly the most sensitive area in your partnership with the consultant.