Hey! That sounds like a reaally annoying situation to be in, so I hope you can find ways around it
I've just finished my Hinduism case study but I haven't completed my notes, so maybe I'll try and post those when I've got them done in a week or so. In terms of advice, the thing that stands out most to me in this part of the course aren't the actual beliefs themselves, but rather the nature and impact of belief systems on individual lives and society, so I wouldn't recommend focusing on remembering all of the names of Vishnu's avatars or the holy texts. Nonetheless, having some examples of the historical background, traditional values, and customs of Hinduism is really important, like understanding the role of the Brahmin or the significance of bathing in the Ganges River so you can apply this to how Hinduism has had a pivotal influence on society and culture. What our teacher keeps reiterating is the conflict or issues provoked/encouraged by Hinduism, such as in relation to the caste system, the oppression of women, westernisation/the loss of Hindu identity, tensions with Muslims etc. so I think it'd be important to know them! If you aren't being given resources on these issues in class, I'd definitely recommend doing some of your own research. Hope this helps!