think of your juices as building blocks. What is each fruit contributing to produce a hedonic/ pleasing blended country wine? ,,, and what is missing that you need to add from the chemical bottles?
Elderberry; my harvest is high on bitter/ tannic flavors, OK on total acidity, it is low on pH, low on sugar and aromatics. I really like elderberry mixed with concord since my concord is good on aromatics and acid and zero on tannin. (Several years; pH 3.91-4.81/ TA 0.67-0.78%/ grav. 1.029-1.052)
Cranberry; interesting long flavor notes, no actual tannin, good aromatics, exceptionally high acid and low on sugar. Looking at this part of the country eating apples blend well since they can be low acid, low on long flavor notes and moderate on aromatics. ,,, I would look for any low acid juice to blend with cranberry. (Several batches; pH 2.6-2.8/ TA 2.8-3.2%/ grav 1.038-1.040)
Pomegranate; astringent long flavor notes which I want under 25% of a mix, nice pH, TA is a bit high, nice sugar level, nice fruity flavor. (One sample pH 3.13/ TA 1.59%/ grav 1.080)
I always try ratios out in a test system before tieing up a carboy for a year, a pie ,, yes I have made elderberry and cranberry into pie with other fruits as apple.