The question of how to balance all three sports is one that has plagued triathletes for ages. Or at least since the 70's when the sport "officially" began!
It's why we call it the "Sport of &"! Swim AND bike AND run.
To appropriately train we like to put different focus on the sports depending on the time of year.
Before the season we'll do "blocks" of each individual sport. Typically six weeks and based around the weather. Six week swim block when it's cold outside, six week running block as temps rise, six week bike block when the spring sunshine arrives.
There is no "balance" between the sports during these blocks. It's 4-5 times per week on the focus sport, 1-2 times per week (maintaining) on the others.
Then as the season begins, we shift to each sport 3 times per week, giving each similar attention with a lot of bike/run bricks worked in, to get more sport specific.
If you want to throw in an additional session of the three during the week we've found an additional bike session to be most beneficial. The stronger you are on the bike, the stronger you'll feel on the run.
What about you? What does your schedule look like as you balance training three sports?