Handling gaps in the knowledge and skills of your team is something that every business owner must deal with, whether you hire only contractors or employees. There are ways to deal with it that work well without offending anyone. Just be honest and up front at all times and your team will follow your lead.
Identify Future Needs
It's important to know what types of projects are coming up in the future so that you can identify potential gaps in the first place. If you know what types of projects are upcoming, you can let your team know so that they can also be aware of the types of knowledge and skills are going to be needed if they want to work on the project.
It can be risky to offer training to contractors, but if you really like working with certain people you can offer regular training to them so that they can learn the skills needed to work on future projects.
Hire Someone New
If you have identified knowledge and skills that are needed now or will be in the future, get serious about making a better description of the skills needed in order to find a new contractor or employee.
Make Them Aware of Training
You don't always have to offer training, but if you know what type of skills you would like for your team to have, you can at least tell them about training that is offered by other people.
Send Them Regular Industry News
Create an email list just for your team where you'll share industry news, training, and other things that can help them learn more about the industry that you're all taking part in.
Offer Regular Feedback
When anyone on your team submits a project, be sure to try to send feedback about what they have done well and what they should improve upon. This is a good way to encourage their own learning on their own time.
Encourage Team Members to Work Together
Some team members are going to know more than others. If you make it possible for them to collaborate on projects coffee with espresso together, one can learn from the other.
It's important from day one to set expectations for your team members. If they realize that continuing education is important to you, and they like working with you, they're going to be a lot more likely to seek out training for themselves.