What, if anything, can be done about venous insufficiency in both legs?

Venous insufficiency. You need to work with your clinician to find the best compression stockings that will work for you long-term. Observation and report of clinician findings over time are the best way to monitor: ulcers, discoloration, pain, inflammation, measurements of the legs, etc. Sometimes, surgery is necessary and you can be referred to a vascular surgeon that specializes in vein surgery.
Treatment. In the short term, compression stockings (at least 20-30 mm hg) can help. Ultimately, you need to see a vein specialist who can do an evaluation of your situation and make a treatment recommendation for you.
Usually yes. Vi occurs when there is pooling in veins, causing varicose veins, & leg swelling, inflammation, & ulceration. Most common cause is when the one-way valves don't work well, leading to venous reflux, or back flow, with blood pooling in the veins. Treatments include compression, medication, and various vein treatments depending on the specific findings in your case. See a phlebologist vein specialist.