I first went to Chiang Mai about 30 years ago and it was a very quiet place then. You could walk across the street unharmed with your eyes closed. I have just returned to Bangkok from Nan and it was almost the same. (Apparently there is a local speed limit of 20 kph there but there is almost no traffic). Staying in the one place means that your parents will spend more time traveling so I suggest you to spend a few nights in about 2-3 places besides Bangkok. Chiang Mai is one place that should be on the list. Sukhothai is another that you should consider. I was really amazed at Nan. Selecting a few places in that are would be a good idea. There are good bus connections between them.
AC rooms at about 500 bahts a night are common. There are low cost plane connections to many places in the North which will help your your young parents. I traveled by bus.
I agree that you should take your parents around as a bit of local knowledge always helps.
555 - ha ha ha - is Chinese as well and suggests "good luck". The minimum price for lottery tickets was AUD 5.55 for several years until recently.
Paul
