Well your view on aerobics and running is very skewed because you were a pretty phenomenal runner. The aversge person could never do sub 20min 5ks or keep the pace you do on longer runs. Your in awesome aerobic shape.
I really dont think you need to do much distance running to stay in good shape for tough mudders. Try keeping your lifting fast paced, do some metabolic conditioning and sprints and maybe twice a week go for runs, one longer run and one 5k. For the 5k, always try and and beat your time.
I understand your obligation to the kids but remember your health comes first. If you continue getting up to pee at night, you will really ruin your sleep. Keep an eye on it.