Thanks in advance for any thoughts.

I have a 7 consecutive night Marriott certificate (from the Marriott air+hotel package) that I am looking to redeem at Bangkok Marriott Hotel Sukhumvit but I am wondering if I should just discard a night or two and extend our stay in Chiang Mai. Taking my mom and sister - it will be their first time to Thailand, my 2nd time to Bangkok. My sister and I are pretty active travelers and like to explore from morning to evening. However my mom is older and is more of a relaxed traveller. We will be in Tokyo for 3 days before Thailand and a long layover in Singapore before flying home to CA.

Rough itinerary as follows and the days/nights in question are in blue:

Night 1 - arrive to BKK around 11pm
Day 1/Night 2 - rest/relax, explore the surroundings, eat and eat and eat
Day 2/Night 3 - Floating market
Day 3/Night 4 - Temples, Grand Palace, more sightseeing
Day 4/Night 5 - Ayutthaya

Day 5/Night 6 - Bangkok (no plans...) or fly to Chiang Rai (explore surroundings)?
Day 6/Night 7 - Bangkok (no plans...) or Chiang Rai (Golden Triangle)
Day 7/Night 8 - If we stay 7 nights in Bangkok, we will fly to Chiang Mai and fit Golden Triangle and Wat Rong Khun into a day trip from CM or Chiang Rai (Wat Rong Khun)

Day 8/Night 9 - Chiang Mai (explore Old City and Sunday night market)
Day 9/Night 10 - Chiang Mai (open or cooking class)
Day 10/Night 11 - Chiang Mai (Elephant Park)
Day 12 - checkout, flight from CNX

Thank you again for your time and responses. Open to suggestions, critics, anything! Thank you!