Access and maintenance

I have sorted child maintenance for my 13 year old. His dad is supposed to pay 70 something a week, plus back pay from next month. He has now tried to sort it together and agree to less He also wiped the back pay with child maintenance. (I have tried all this time and only asked for 50 so he lost that chance lol) But him and his wife have spoken to solicitors and want me to agree to ' facilitate access" meaning I have to do half the journeys. I go up to Watford, where he lives most school holidays and stay with my nan so my son can see his dad. His dad has done the journey here once this year. But he is saying he wants me to agree to bringing him up on a regular routine, every other week or even weekly. He obviously wants his maintenance lower and knows if he sees him more, that will affect it. But I would spend more than that getting him to Watford My question is Do I have to travel up there as of when we agree? He sounded almost threatening, like I would be in trouble if I didn't and the fact that I've got two young children as well as our teen wouldn't affect that