My dad is bipolar and my daughter's brother in law is bipolar as well. Does this familial history make it more likely her child will be bipolar?

Bipolar heritability. I wouldn't worry excessively in this sutuation. Although bipolar disorder is a genetic illness, we usually worry when the parents or the siblings have diagnosed bipolar disorder. I would also worry if the child's both grandparents and a few second degree relatives had it. On either case, i would keep my eyes open for any possible signs of bipolar presentation in the child.
Yes, it does. Bipolar disorder has a strong relationship to family history. It is important to be aware of this family history and to share it with physicians, as sometimes bipolar presents only with depression. The medications used for bipolar depression are different. With bipolar disease on both sides, it makes that disease possible. But it is not at all 100%! so don't be too worried until something shows up.
Not as much as. the going rate for the case of the following: 35% or so a child will have it if one parent has it 75% if chance child will have it both parents have it. But I would say only somewhat greater than the chance of the general population that does not have bipolar disorder in close but extended family. A supportive family can reduce stress & expression of bipolar and the opposite is true. .