how did you manage no sleep with infant and prechooler??

I have 2 kids but my oldest was 10 when I had my second and in school and able to do for herself. I am going to have a 4 year old and an infant.. how did you handle the lack if sleep obviously I will not be able to sleep when baby sleeps my 4 year old still gets up at 630 every day

and I know yallhave some tips because some of you have even younger children with infants. all advice and tips. Thanks