At five weeks old, with a social mama...they aren't feral yet! What they are is scared.
TBH the best thing you could do is try to catch them and bring them inside, along with mum, and keep them confined in one room. At that age if you make a point of it, you can socialize them almost entirely in a week or so! Since mum isn't afraid of you if they can't escape they'll watch her and loose their fear quite fast, especially if you give them lots of yummy food when you're there.
If they willingly go into the box with straw sneak outside and try to block the babies in. Then use that to bring them inside into a bathroom. Honestly, if you spend a week socializing them then you could turn them over to an adoption agency at 6-7 weeks and they'll be fully adoptable once they've been vet checked ect.
I've done it! Muffin was 'feral' at 4 weeks when I brought him inside, it took me all of 4 hours to have him snuggling and purring. That was without
his mum helping! (Who was a true feral.)
The first litter I ever stole from their feral mum I took at 12 weeks old. It took me 3 weeks to socialize them to the point that I could adopt them out, and most groups won't even take kittens that age.
The sooner you do this the easier it'll be, I promise!
PS, we totally need pictures!