Closest match: ① They know the person who may give Tom 100 dollars with which he would buy a beautiful dress for his girlfriend Jane. Note, this is overly wordy - technically correct but awkwardly unnatural. There are many ways to be more simple & natural but the meaning would change a bit. For example: ① They know who will give Tom 100 dollars to buy a beautiful dress for his girlfriend Jane. ② They know the money which Tom's teacher gives him with which to possibly buy a beautiful dress for his girl friend Jane. ^ This is technically acceptable. But there are subtle issues that a native speaker would often fix. Here's my version: ② They know the money that Tom's teacher gives him with which to potentially buy a beautiful dress for his girlfriend Jane. Note: Instead of repeating 'which', I replaced the first one with the more common & easygoing 'that', for a smoother sentence. 'Which' is a high-stress word, used like strong finger pointing, so it's best to avoid using it more than once in a short phrase. Also, I changed 'possibly' to 'potentially', not because 'possibly' is wrong, but because 'potentially' is a more relevant, focused, smooth & mature way of speaking in this context. ③ The money with which they know Tom would buy a beautiful dress for his girlfriend Jane, if provided by his teacher. ^ This is the most basic and direct correction, with minimal changes. ③ The money with which - if provided by his teacher - they know Tom would buy a beautiful dress for his girlfriend Jane. ^ This is a more sophisticated way of speaking, but good for written work. Note, the dashes can be swapped for brackets to make it less formal and more accessible to less educated readers.

I'm no expert, but each of these 3 sentences sounds unusual to me.🤔