The family court seems to be a twisted parallel universe in which the rights of abusive NRPs are prioritised over the safety and wellbeing of everyone else.
If children resist attending contact, it's the resident parent's fault. If they tell social care about the abuse they suffer during contact, the RP is admonished for parental alienation.
If the RP keeps a diary, they are accused of evidence gathering. If they seek support for the distressed child from professionals, they are accused of fabricating.
If safeguarding concerns are raised by schools about what the children say about contact, the facts are misrecorded/twisted and then lost in the mists of time.
Even when abusive NRPs admit to having been abusive, they are given chance after chance to prove that they have learned to be better parents.
All the while, the children are becoming more and more damaged, the abuse of them and the RP continues and there is nothing anyone can do to stop it.
I don't know the solution but I do know that the recent thread about making parental alienation a crime is terrifying. It would just empower these abusers further.
OP, I'm so sorry you're in this position. Please make sure you are very careful not to say anything to you DCs that could be used to justify any accusation of parental alienation.
Please do make sure you have someone with you for any pick ups. If you can afford it, a CCTV camera protecting the front of your property that can record interactions at the front door could be helpful.
The meltdowns sound horrific but they are only happening because your DC feels safe with you. DC will know that you are always there for them and in a few years, will have the right to refuse contact.
Sending hugs and 
It is shit but you will get through it and your DC will always know you were there for them in every way possible.