While it is not unusual for a lay person to be invited by a parent or family to attend an IEP meeting, the participation of such persons can be challenging. If you have information that the family may find helpful in understanding what the school staff are doing or what they are likely to do, I recommend that you share this information with your friends, but stress that they need to ask questions of school staff rather than make assumptions based on various sources.
This sounds more like a disciplinary meeting than a regular IEP session. I would encourage you to help the family located an experienced and qualified attorney or education advocate to assist the family and the child deal with the school staff. Sometimes the best recourse is to have a qualified professional participate in the IEP when serious issues such as discipline, physical contact with the child and placement options are at issue. Good luck with this.
This is not a substitute for a consultation with an education or disability rights attorney in your community.
I would strongly advise your friend to retain a special education attorney like myself or an special education advocate to attend an IEP meeting. IEP meetings can be quite complicated and unless you are experienced, trained or knowledgeable in special education then yoru questions will probably not eliciit the information that is designed to develop an appropriate special education program for this child.
A parent can invite another person to the IEP meeting that has some specialized knowledge or experience with the child to render opinions or ask questions concerning the development of the child's IEP.
Parents have the right to bring another person to an IEP meeting, but there are no specific rules as to whether and to what extent a non-professional can participate. If your son is being restrained, that is a serious issue and may be a symptom of an inadequate program. You would most likely benefit by consulting with a special education attorney in your area to discuss the legal .