What are my chances of multiple birth if I am twin & my husband has a twin sister?

1.5-3% Risk of twins with a family history is slightly increased to ~1.5-3% from baseline 1.5%. Exact risk may also be due to other factors besides family history, such as age of woman, ethnic background, baseline fsh level. However, the family history of twinning on paternal side contributes little, if any at all, since its the number of eggs released by the woman which usually determines twinning.
About 1% Fraternal twins are from ovulation of two eggs, and identical twins less commonly from an embryo split. There is a gene for multiple ovulation, so twins can run in families, but this does not often happen. There is little familial component to identical twins. Your husband's history won't play a role. It's likely that your risk of twins will be similar to all other women, that is about 1%.