ALA is an essential fatty acid, meaning that your body can’t make it, so you must get it from the foods and beverages you consume. Your body can convert some ALA into EPA and then to DHA, but only in very small amounts. Therefore, getting EPA and DHA from foods (and dietary supplements if you take them) is the only practical way to increase levels of these omega-3 fatty acids in your body.
In your final paragraph, you suggest that a ratio of 2:1 EPA/DHA maybe best for reducing inflammation. Are you suggesting using two separate products to obtain that ratio? I can't see how it is achieveable through standard omega-3 products. Good fish oil brands are typically 60% or higher EPA, but never reach a 2:1 ratio in my product searches. According to case studies (link below), 1 gram of EPA per day (60% or more of the total omega-3 content) is sufficient and the highest efficacy.
After a large number of lab studies found that omega-3 fatty acids may be effective in slowing or reversing the growth of hormonal cancers, namely prostate and breast cancer cells, animal and human epidemiological studies have been conducted to see whether this effect occurred in real-life scenarios. The evidence is somewhat conflicting in some reports, but there is some evidence to suggest breast and prostate cancers may be potentially slowed (or the risk reduced) in people who eat a lot of oily fish and possibly those who supplement with omega-3. (66, 67, 68)
Fish oil is FDA approved to lower triglycerides levels, but it is also used for many other conditions. It is most often used for conditions related to the heart and blood system. Some people use fish oil to lower blood pressure, triglycerides and cholesterol levels. Fish oil has also been used for preventing heart disease or stroke, as well as for clogged arteries, chest pain, irregular heartbeat, bypass surgery, heart failure, rapid heartbeat, preventing blood clots, and high blood pressure after a heart transplant.