Gestation time is 3 months, 3 weeks, and 3 days. Sows will go into heat (breeding time) within a week of piglets being weaned from her. I can't tell you how long feral pigs nurse before mom weans them off.
As long as those little ones are nursing, momma won't get pregnant again. Aim for mom first. If she goes down, wait a little while. The young ones will come back to a dead mom to try and nurse. Then round up the piglets.