Ditto, I wouldn't even attempt to remove these without an air impact wrench. They are unique bolts, screwed into nuts welded inside the frame. If you strip or break either, it becomes a real mess to fix.
Spray alot of penetrating oil on the bolts before attempting to loosen them. I broke one of mine in an attempt to remove the crossmember so that I could get out a lower control arm. I tried drilling it out and only got so far as it is hardened steel. So, then I tried using an extractor and that broke in the hole. Back to drilling again. I then tapped threads and put it back together. Waaaaay too much work. Get the penetrating oil and impact driver out.