My family has taken a habit of coming to visit once a year in the summer wherever I lived in Asia. Each year I draft for them an itinerary from 1 week to 1 month. In this travel, they all came at different time and we had just 1 week all together and then I help prepared separate itinerary for each groups. Since my parents had visited already some parts of Thailand whereas for my sister's it was the first time, I had to split them into 2 groups.
This itinerary was slow pace to accommodate for my different ages in our group - from 50-60 years old to my nieces who are 4-10 years old.
Since we travelled with at least 8 to 9 people - booking well ahead of time for mini-van services & private tours is very important. It's definitely a plan that can't be last minute.
We started with some camping in my apartment & usual visits in Bangkok ( Emerald buddha, khlong boat rides, Sukhumvit malls etc... ), followed by a couple of days together in a huge private villa in Cha Am (40min north of Hua Hin) with lots of space and a sea view to spend quality times all together. Since Hua Hin was 40-45min drive from our secluded choice of accommodation - we went only once for the night market, the rest of the time we enjoyed the swimming pool, the sea and the outdoor barbecue.
After this time together, I sent all of them to visit Sukhothai with its beautiful ancient temples. This usually takes about 1 full day with a private tour . The hotel I chose was a small isolated guesthouse/house where I believe my family were the only one. They provided all necessary transfers from the airport and then a private driver to Chiang Mai for all of them.
From Chiang Mai, my sister stayed there for a couple of days to visit the city, take a tour to visit the Doi Su Thep and the mountains, whereas my parents who had already visited this part went on to Laos and stayed a couple of days exploring around Luang Prabang. From Chiang Mai, there are convenient and short flights to Laos.
Everyone then passed by Bangkok to catch their final flights and for final shopping & food indulgence.
My family gave me good comments on all the choices of hotels & itinerary. Obviously my parents are less cost sensitive than my sister travelling with a child - therefore some hotel choices reflect that. Also it was my mother birthday so I sponsored the hotel in Luang Prabang to gift her with a unique experience. ( And secret retreat group of hotels never failed to deliver just that ).