A Mackenzie friend us someone who can accompany you into the court room if you don't have a barrister. You can talk to them quietly for support but they CANNOT address the judge.
You need some solid legal advice. Do not initiate court, with a lawyer and or barrister it becomes hellishly expensive. About £5000 per visit and it will take a minimum of three visits.. One to seek an order and then have it served, second for fact finding and hopefully the third for Final Orders. Any dispute and it can go on and on. So let him act. Oh! and the court will also expect an attempt at mediation before all if this. If anything ask him to attend a mediation session with a lawyer who specialises in mediation.
The rule of thumb is that the court will attempt to maintain the status quo, so if you've established a pattern of contact that you feel is detrimental to yourself it will be difficult to show otherwise
Work out what is good for you, mine has a few hours at the weekend, that's it. Set times, set day.. Set up a burner phone for text SMS only, an email account just for communication purposes. Do not use, whatsapp, duo facetime Allo, telegraph, wire, Facebook messenger or Instagram. just plain old sms. If there is any abuse the police can act quicker as it breaks telephony laws that are well established.
Use a library for dropoff and collection near the desk, if there is any threats then there are sever penalty's for abusive behaviour in a council owned library.
when you are ready and you've had a break from the difficult behaviour, start contact again and STICK to the schedule you ( you not him) have decided on, like;
10 till 4 on a Saturday, with a text 5 mins beforehand confirming, cancellation of contact occurs if 30 mins late with no replacement date, once missed it's missed. There is little you can do about late return, but the court will see that as irresponsible behaviour and an inability to comply with a simple requests AKA being difficult.
The aim of a family court hearing is to establish reasonable and sensible contact routine for the children with the minimum of disruption (and fucking about) where both parents can behave in an agreeable and amicable way.
The hardest thing to get is that little of this can really be enforced, unless a pattern of intimidation and abuse can be shown by the police. Otherwise your stuck with letters at £1000 a pop from your lawyer that get ignored, then your back in court again where the judge says do as your told and they don't.
Quick summary, don't initiate court let him do it. Establish what is a good routine for the DC's and you you are the primary carer after all. Engage a mediator.