Rear shocks / struts

Those look like some J.C. Whitney-quality helper springs, not in any way "struts"
I'd remove the lower shock mount, so the helper has someplace to go, before loosening the lower spring mount.
For new springs? I'd Google "helper springs"
(How are the upper shock mounts? Broken yet?)
I'd be tempted to borrow a spring compressor from Kragen, or O'Reilleys, or whomever. Could also maybe use a bunch of wire ties.