I really could not care less what Nationality the driver is but he really needs to be taught a lesson for what I can only call a really disturbing and disgusting piece of behaviour. As the Lawyer writes throw him in jail for a month. I am absolutely appalled by his behaviour but it does seem almost common here.
This sounds a very reasonable amount to pay for 3 children and their needs. They will certainly not have any luxuries in their lives if you give this amount. I would also say that her parents must be able to support themselves as 5 people cannot live even moderately from that type of income. They sound like good people to me. Plus the value of the Baht is strong so that makes this amount seem surprisingly low. Whatever happens I wish you the very best for your future together.