Beginner in Malaysia

[Catriona]

Selamat datang ke Orchid Board!
The roots on top of the pot - arial roots - will always be silver, unless you have just watered them, as in pic. 3, and are not a good indication as to whether your orchid needs watering. Cntry's suggestion to check with a skewer is a reliable method. You may find, given the high humidity in Malaysia, that they can go for longer than 7 days. Humidity is more of an issue than heat; growers in a very dry heat would, I think, have to water more often than 5-7 days.
I am quite new to growing orchids myself, and those with more experience will be advising you, but personally I would remove the flower stalks on each orchid. Whether they have buds or blooms, they are diverting energy from the leaves & roots, & your orchids look like they need all the energy they can get. The orchid with crown rot is probably a goner - I had one in exactly the same state and eventually I had to throw it away. Keep trying, though - you may yet get a keiki (baby plant).
Malam yang baik dan semoga berjaya.
[I said good evening & good luck]
Cut the stems with sterile knife/scissors & dab powdered cinnamon on to cut edges, to stop infection.