What is the likelihood of me getting bipolar if most of my family have it?

Increased, how much? Almost every study i've read says, "increased" risk - few put a number out. Here's one that does - i can't vouch for their accuracy, but they say heretability is 60-85%. Risk is only 1-1.5% in the general population, identical twins~65%, fraternal twins ~20%. But, keep your eye on the target - it's a growing field of inquiry and the condition itself is still being defined as we type. Imhro.Org.
Maybe, maybe not. Research that focuses on the children of bipolar parents provides a wide range of estimates of likelihood of getting bipolar or another mood disorder, roughly 40-70%. Depression seems most common. But it's also hard to tease apart the purely genetic causes from the effects of being raised in a family affected by the parents' illness. The better care they took of themselves, the better for you.