Day 1: Grand palace & Emerald Buddha temple (within the palace)
This place needs about 4-5 hours to see the Grand palace, The Wat of Emerald Buddha inside the palace, the murals and the intricate architecture. You will have to wear full pants/skirts and sleeved shirts/tops (that is cover your legs till the ankles and your arms) to enter the complex. Shirts & sarongs available for rent at the entrance, in case someone is wearing shorts/is sleeveless.
Day 1: Wat Pho (Reclining Buddha)
This is very close to the Grand palace and can be clubbed with Grand palace. Ideally, start your day with Grand palace, break for lunch and then do Wat Pho (picture below, of a line of Buddhas) and the finish the day with Wat Arun (next).
Day 1: Wat Arun
From Wat Pho, you can walk across to the river bank (Chao Phraya River), to Wat Arun. There are water taxis to get you across to the other side of the river.
Day 1: Others
Since you have seniors and kids, these three places should be enough for the day. Any more could make the day too packed.
In the event some of you wish to see more, there are some more places to see in and around the Grand palace area and so can be done on the same day:
a) City pillar shrine (opposite the Grand palace) - can pass by this place, don't think it is worth a stop unless you absolutely feel the need
b) National museum - again at a 5-10 mins walk from the Grand palace
c) Wat Saket (10-15 mins from Grand palace): this one requires a bit of a climb (stairs) and provides a great view of the city from the hill
Day 2: Day trip off Bangkok - Ayutthaya
You can book a private tour to Ayutthaya (the ancient capital of Siam and a UNESCO world heritage site now). This is both historic and spiritual. The drive outside Bangkok is beautiful through the countryside & lush paddy fields will keep you company.
In Ayuthaya, you can see Wat Phra Mahathat, famous for the Buddha head embedded in a tree’s roots, Wat Phra Si Sanphet, with its three dominant chedis, Wat Ratburana, and Wat Chai Wattanaram. It is fun to cover Ayuthaya on an elephant. Especially, the kids will enjoy it. Most private tours cover Ayuthaya and the Bang Pa in summer palace. If you take a private tour, you can pace your day according to the needs of your group.
Day 3: Day trip off Bangkok - Tiger Temple
The temple of tigers at Kanchanaburi is where you can walk with, pet ND feed tigers. Kids will love this. Actually everyone will. Again, take a private tour will be great for you.
Day 4: Floating market (photo of one below)
You can do this in the morning. There are many floating markets but the most recommended one is the Damnoen Saduak floating market. It is interesting but a caveat - it is very touristy. If you start early (say by 7.30 or 8 am), then you beat the crowds that come in by 9 or 10 am. There is another one - Amphawa Floating market. I have heard it is less touristy - but I have not visited it.
Day 4: Siam Ocean World
This can be done in the second half of the day. The kids will love it. Some of grown ups in the group can possibly use this time to relax/shop/walk around
Some other suggestions not included above
a) Jim Thompson Thai House: Sort of a museum of arts/Thai heritage with old Thai houses. It gives you a good flavour of the old world Thailand. It is very close to Siam Sqaure/MBK/ tc - which are the prime shopping places so you can choose to split the group, if required.
b) Cowboy Soi: If you wish to experience Bangkok (a little sleazy perhaps) nightlife, this street is THE place.
c) Chatuchak weekend market: Apart from the usual MBK/Siam sqaure area shopping, I would recommend a visit to the Chatuchak market if you are in Bangkok on a Sat-Sun. This place is not really touristy, usually locals shop here for everything from home decor, household items, cheap electronics, pets, kitchen ware. It is like a huge expo ground, very colourful and interesting and with great deals (eg - souvenirs, vases, articifical flowers, cutlery, cheap electronics like bluetooth speakers/mobile accesories/fancy electronics/etc)
More on markets in Bangkok
a) Chatuchak Weekend Market: Weekend Market with 30-40 aisles (would take anywhere from 2 hrs to 10 hrs depending on what you what to experience). Everything from cutlery to furniture and from pets to electronics are sold here.. Only on Sat-Sun, though.
b) Damnoen floating market: Sells flowers, vegetables, food - ideal time to visit is between 7 am and 11 am
c) Pak Klong flower market: A variety of flowers - local and imported are sold here. It is a visual treat, even if you do not intend to shop for flowers
d) Rod Fai market: Interesting vintage Market - everything vintage - vintage cars, antique furniture, antique knick knacks are sold here
e) Pratunam market: Clothes - at wholesale rates
f) Ratchadapisek night market (Vespa market): A very happening night market and has a display of vintage vehicles - Vespas, VWs, Austins, etc. From 5pm to midnight, on Fridays and Saturdays.