I looked up talk = बात vs speak=बोले and it seems बात is more like a noun than a verb (e.g. a talk, a matter, an idea) and is the verb as करते= "do or engage" , so for me (native English speaker) to remember the Hindi I see it as "Raj and Aamir do the talk a lot." What's the difference to a Hindi speaker between "राज और आमिर बहुत बात करते हैं।" and "राज और आमिर बहुत बोलते हैं।" ?
In Hindi, nouns and adjectives are frequently turned into verbs by tacking on the verb करना (to do). Eg: पसंद करना (to like), इंतज़ार करना (to wait) etc.
So, even though बात करना is literally 'to do the talking', it just works as 'to talk'.
राज और आमिर बहुत बात करते हैं - They talk a lot (ie, have a lot of conversations). This may be among themselves or with others.
राज और आमिर बहुत बोलते हैं - They speak a lot (ie, a lot of words come out of their mouths).
The main difference is that with 'बात करना', it's usually a two-way conversation while with बोलना, it's one-way speech. In addition, बोलना may also be used as 'to say'. When you're discussing something with your boss or chatting with your friend, use 'बात करना'. With a parrot saying something, a speaker giving a TED talk or when you're telling your mom about your last vacation while she is just listening, use बोलना.
In addition, you also have the words बताना and कहना that are similar to 'to tell' and 'to say' respectively.