The phrase “fix it so he could” conveys very little information (it essentially means "make / let him", perhaps like 让他) . We can safely simplify the whole sentence to: At the time they buried him, placing him next to all three of his women was impossible. or even: They were unable to bury him next to all three of his women.

“when they came to bury him, they could not fix it; so he could lie next to all his three women. " Or " when they came to bury him, they could not fix it so that he could lie next to all his three women. "