The fact that your friend's ex has a residence order doesn't change an awful lot. By and large it is a label.
You say she has been excluded from important decisions but it is important to remember that a residence order does not confer the ability of the resident parent to do this. Your friend will have parental responsibility which means she has a right to be involved in her childrens' education, health, etc. and courts generally will not be impressed that she has been excluded.
As a holder of PR she has a right to be consulted'. It is important to realise that this has limited value - a non resident parent being <span class="italic">told</span> about these decisions would arguably be described as being consulted'.
I would disagree with the solicitor's advice you mention. There is no such things as custody' or residence' and in my experience your friend would be very unlikely to get a court to order that a child live with her.
If her ex will not attempt mediation she cannot make him. She should consider carefully what she wants to achieve. Assuming it is more involvement in her childrens' education it may be better for her to contact the schools, doctors, etc. directly advising she has PR and ask that she be sent information about school trips, medical information, etc. Do not be surprised if she is told they cannot do this because they have been told not to/she isn't allowed/she need's her ex's permission.
She doesn't.
She has PR. The only way she would not be permitted this information is if there is a court order specifically stating this.
I would also recommend she joins Families Need Fathers. We have an increasing number of mums who are dealing with this situation which has usually been more familiar to dads.
Hope this helps.