I wouldn't use the term workshop because it would seem to imply that there is a certain physical activity which takes place during the gathering of the members.

Here are some definitions of workshop found on the web:
- Similar to a seminar but with a greater degree of attendee participation, interaction, and hands-on exercises.
- a set of activities designed to promote learning, discussion and feedback about a topic or event
- A brief intensive interactive educational program, generally for a small group of people, in which the content is practical and specific to the needs of the group. It has objectives and may concentrate on the acquisition of specific information or skills.
A workshop is a series of educational and work sessions. Small groups of people meet together over a short period of time to concentrate on a defined area of concern.

Training:
- Training refers to the acquisition of knowledge, skills, and competencies as a result of the teaching of vocational or practical skills and knowledge that relates to specific useful skills.
- To make proficient with specialized instruction and practice.
- The systematic process of developing knowledge, skills, and attitudes for current or future jobs.

and finally seminar:
- A class that has a group discussion format rather than a lecture format.
- Most commonly offered as upper-level and graduate courses, these are small classes of approximately 15 students each, designed to facilitate intensive study of specific subject areas.
- Meeting or series meetings of specialists who have different skills but have specific common interest and have together for training or learning purposes. The work schedule of a seminar is aimed at enriching the skills of the participants.
- An oral presentation on a specific topic. The discussion may include a contribution from staff. Where the presentation is by a student, the seminar may form part of the internal assessment of a paper.

So finally to conclude. In my opinion the term 'seminar' should be used if the participants will concentrate on theory rather than practice.
The term 'training' should be used if there is a mixed variety of activities i.e. learning and practical application of the acquired theoretical knowledge.