Should I stop?

I babysit my two nephews currently as a job and they're a handful. Their mom works from home so she's usually always here and every time the youngest one (Dev; 1 year old) sees her he starts crying bloody murder, which is very frustrating. The older one (Jax; 4 in Sept) just doesn't listen and also always wants mommy. I'm having a baby in September and I'm not sure if I should continue watching them after my son is born. Dev constantly wants to be held and I'm not sure that will be possible with my little one, but they both throw tantrums whenever they don't get their way. Jax will be beginning school then but it is only three days a week and I'm not sure if I can handle three babies at once. Any advice?