My concern with individual KPIs is that Management Systems talk about processes - when there is a discrepancy, it is something in the process, not the person. Individual metrics have the potential to send a message contrary to that philosophy.
To further this point, consider the difference between 'accountable' and 'responsible'. I may be required to complete an activity but have no ability to ensure that it is done on time and in spec. So, if there is a bottleneck that adversely impacts my ability to complete my task and I have no authority to resolve it, I will be unable to complete my responsibility and there goes my KPI. It can be a frustrating and demoralizing scenario, and set the entire team up for failure.
Are you trying to improve the performance of individuals or the performance of the team?
If you're looking to focus on the individuals, it's important for everyone to clearly know what the expectations are regarding competency. Where gaps exists, the right enablers (e.g., training, mentoring, coaching, job shadowing, etc.) should be provided if you wish to provide them with the opportunity to improve.
Keep in mind, however, that not everyone wants to change or improve. Some people are perfectly content to come to work, meet expectations and go home. Their priorities in life are elsewhere. This is neither right nor wrong...it simply is.
If you're looking to focus on the team as a whole, I recommend you read Patrick Lencioni's "The Five Dysfunctions of a Team". There is a self-assessment in the back. Recently, our team had a team building and planning day. We've experienced a lot of change with our team dynamic over the past year and we're also experiencing fatigue and burnout. Prior to this team day, we had all members of the team anonymously complete the self-assessment. We showed the results at the team meeting and had some interesting discussions regarding our team and our roles within the team. Feedback afterwards was that this was a value-added discussion and helped individuals to regain trust and focus.