Not sure what to do?

I have started a school run with a little boy for the first time. As I have 3 under 3, and a new 3 year old, and no car, when asked to do this I said I would only do one way, as I worked out (walking and bus trip), it would take me an hour there and an hour back.

I asked the other parents and they are fine with it, as long as babies aren't in the wind/rain etc. They trust me thankfully! I got the parents of the little boy to sign they were happy with this, and that I would phone one of them to fetch him should the weather be too bad to go out with 4 little ones. They readily agreed and signed.

This week I had to call for the first time - was pelting down outside, winds were high. Mum unavailable on her mobile. Dad got snotty on the phone with me, mumbling 'I knew this would be a problem, you know what would solve this? Their mother should be home with them! And this will only get worse as we head into winter'. He is often a bit sarcastic when fetching the kids anyway, and mum does most of the lifting. I didn't tell her about his complaining to me though, even though I thought it inappropriate. I did not want to casue any unnecessary tension, as I know she'd be upset with him if she knew he'd said that to me.

I have to push lunch and sleepytime an hour earlier for everyone, and the run takes most of the whole afternoon, so I am being VERY flexible for them, and want to help very much, but I do not need attitude at the end of the day. It's easy for him, he jumps in his car with his one child, and it takes quick quick. A totally different story for me.

I am stuck though as to what to do. After chatting with my sister this pm I think I'll give it a couple more weeks and then decide whether to continue or not. I'll also ask the mum if she has befriended any of the mums and if any live close by and could drop him off after nursery. I just feel in such a pickle. I don't want to let them down, but I have other kids to think of too! Plus I don't appreciate the complaining on the phone - he is obviously having issues with his wife working (she's been back at work for a year)... but the childminder is NOT the right ear to mention this to... no matter how well he thinks we get on.

I am not being funny, but as much as I love the kid, I have a waiting list and them leaving, although not ideal as I love him to bits... would not be a train smash for me business-wise, but he is so happy with me and all has been so lovely till this school run, and having all the kids so young and the run taking so long...