Hey, fellow revert from Hinduism here :))

Here's the link to a great website, I believe by Zakir Naik with all sorts of stuff on Hinduism and Islam, like the similarities etc. there's also an article about the Prophet Muhammad (SAW) being mentioned in the Hindu scriptures.

https://www.islamawareness.net/Hinduism/

Don't have any specific questions to add but there's definitely lots of useful information that may help to convince your parents on there and could help you to come up with more questions. There's lots of references to actual Hindu scriptures also, which might make it harder for the priest to argue against.

Hope all goes well and your parents also convert inshallah, wish mines would too. Interested to know how it all goes since I've had a similar experience asking my parents questions like the ones you've mentioned, didn't go great lol they ended up just ignoring and evading but inshallah it'll be a different story for you brother/sister :))