Yes.

需要我擔保他們嗎？

-If they show they have money to cover their travel fee, you do not need to 擔保他們. Otherwise, you need to provide I-134 to support their travel financially.

若出問題（比如生病看醫生），是不是當他們負擔不起時，最後由我埋單？

-I am not really sure about it because they are not immigrants, and there are different arguments.