Too overwhelmed to watch our kids

Anyone elses SO get too overwhelmed to watch the kids?

I work a couple days during the week and every other weekend. On the weekend my fiance watches the boys (toddler and infant) and every time he texts me telling me I need to come home, hes going to lose his shit and that they wont stop crying.

During the week when I work my parents watch the boys for a few hours and every now and again my parents ask that my fiance bring them, (I go into work at 3 and he goes in at 5)

(due to doctor appointments, cooking dinner and just daily life things that are easier to do without kids around and they have a right to ask that of us considering they are gracious enough to baby sit at all)

Anyways as of lately every time I ask him if he can bring the boys to my moms before he goes into work he all of a sudden has to go into work early and cant do it. Every. Single. Time.

Where as I want to be understanding and sympathize with him, I'm also starting to get frustrated. I dont think he just doesnt want to watch the babies (which my mom thinks it is) I think he just gets super overwhelmed with them. I'm really not sure how to get him more comfortable with it other than just to face it and do it. Anyone have any suggestions or been in this predicament?