My fianc� pregnant with twins 35 weeks tomorrow they are mono di twins and very healthy?

Two weeks ago they were 3.13 and 4.07 my Fianc� was only gaining around a pound every 2 weeks now in two weeks she went from 166 to 171 and feels alot of pressure from baby A (Sadie) who was Always very low and baby B (lily) Is high now for the past couple days she's been getting really bad cramps in her legs and feet and yesterday she way getting lower abdominal pain she said like very bad period cramps also made her feel like she had gas but it went away but I'm just wondering if anyone can guess at how soon my little girls could be here