Within one week's time, two leaves on my orchid turned completely yellow. Why?
If the soil is not too wet, this will give you some other reasons:
https://www.gardeningknowhow.com/plant-problems/environmental/plant-leaves-turn-yellow.htm
Can Orchids be planted in the same pot together? If so, must they be the same 'type' of orchid?
Orchids that need similar care can be planted in the same container. You will need to make sure that they need the same light, humidity and food.
What type of soil? How often do you water? How often do you fertilize? Pot type and size?
These articles should be of some help to you: https://www.gardeningknowhow.com/ornamental/flowers/orchids/indoor-orchid-care.htm
https://www.gardeningknowhow.com/ornamental/flowers/orchids/make-orchid-bloom.htm
I overwatered my orchid (I think) and all the flowers fell off within 2 days. Cannot think of another reason this would happen? What next?
Overwatering can cause this to happen. But, it should not kill the plant. With some TLC and the right conditions, it should bloom again. This article may be helpful to you:
https://www.gardeningknowhow.com/ornamental/flowers/orchids/make-orchid-bloom.htm
Can you tell me what to do with a keiki that has been left on the mother plant too long? The roots are more than 2 inches long. They are about seven inches. :(
That is ok, you can go ahead per the directions. The 2" roots are the minimum amount of roots you need to remove the Kieki. If you have more, this is not a problem.
Just in case you need it, here is the link to the article:
https://www.gardeningknowhow.com/ornamental/flowers/orchids/orchid-keiki-care.htm
My daughter passed away recently and she loved orchids. I would like to plant some near the site she lost her life. Can orchids be planted outside?
I am so sorry to hear of your loss. There are many types of orchids that can be grown outdoors with the proper care and growing conditions. This resource should help with choosing one best suited for your area and how to care for it: http://everything-orchids.com/outdoor-orchids
Can you provide information on how to water orchids and what type of fertilizer can be used? I live in Sri Lanka.
This article should help you:
https://www.gardeningknowhow.com/ornamental/flowers/orchids/indoor-orchid-care.htm