In family proceedings a McKenzie Friend sits beside you, helps with papers and takes notes. The court's permission decides everything beyond that: speaking roles are granted case-by-case under the Practice Guidance, and judges vary widely in how much they allow.
The guidance requires: the MF has adequate experience, no interest in the case, understands the confidentiality duties, and the court is satisfied. In practice: hand the judge a short written request (the Practice Guidance template), state your MF's experience, and accept a refusal gracefully - many judges prefer to hear you directly with the MF prompting.
The night before: bundle tabbed and paginated, a one-page chronology, a one-page position statement, and a list of the 3 orders you actually want. Agree hand signals for 'you're drifting'. Their job in the hearing is notes and prompts - yours is speaking, slowly and to the welfare checklist.
Sit with you at the bar, take notes, help organise the bundle, prompt you quietly, and make submissions IF the court grants a right of audience. They cannot manage your case outside court or act as your agent - correspondence goes to you, not them, unless the court orders otherwise.
For litigants in person facing an opposed hearing: usually yes - the preparation help alone (chronology, bundle tabs, position statement review) changes how you present. For short uncontroversial directions hearings: often unnecessary.
Yes - anyone with your consent and the court's permission (rarely refused for family members) can act. The only standard exclusions are people whose own conduct is problematic (e.g. someone subject to a restraining order involving the other party).
Disorganised bundles, rambling positions, refusal to focus on the child's welfare, unagreed late evidence, and McKenzie Friends who turn the hearing into a second advocacy contest. Preparation is the antidote.
Court fee for a C100 application (currently £232 in England and Wales; verify at time of filing) plus your own preparation costs - solicitors run to thousands, McKenzie Friends to hundreds depending on hearing count.