How do you actually pollinate or cross pollinate Mandevilla to produce seed and new hybrids?
Hybridizing is a very long topic! I have listed a few links for you to help you get started.
http://www.aces.uiuc.edu/vista/html_pubs/PLBREED/pl_breed.html
http://plantdaddy.blogspot.com/2009/12/mandevilla-hybridization.html
https://www.gardeningknowhow.com/ornamental/vines/mandevilla/mandevilla-propagation.htm
Leaves are turning yellow
Here are articles that will help you make adjustments.
https://www.gardeningknowhow.com/ornamental/vines/mandevilla/yellow-leaves-on-mandevilla.htm
https://www.gardeningknowhow.com/ornamental/vines/mandevilla/mandevilla-plant.htm
Potted mandivilla has yellow spotted leaves that die and drop.
Here is an article that will help you pinpoint the cause.
https://www.gardeningknowhow.com/ornamental/vines/mandevilla/yellow-leaves-on-mandevilla.htm
What am I doing wrong? Plants face east. One is fine, the other, not so much.
This article will help you pinpoint the issue.
https://www.gardeningknowhow.com/ornamental/vines/mandevilla/yellow-leaves-on-mandevilla.htm
Should I water the leaves as well as the soil? I live in Taos, NM where we have warm/hot dry winds. Since this is a tropical plant, should I water the leaves as well as the soil?
No, avoid splashing the leaves with water while watering your plant.
If in the case that you have pests on your plant, you can use the hose to spray off the leaves and dislodge the pests.
https://www.gardeningknowhow.com/ornamental/vines/mandevilla/mandevilla-plant.htm
What type of animals eat mandevilla flowers ? What can repel such animals? Will the plant ever reflower? Anything to be done to help it or force it to reflower?
What animals are you having an issue with?
A Mandevilla produces flowers throughout the growing season, so you should see more blooming.
Can you move the plant to a safer location?
my red flowers have white blotches like lack of pigment here and there. Is that a disease?
This is likely due to water spots on the flowers from overhead watering.
Avoid watering from above, instead water at the soil level.
https://www.gardeningknowhow.com/ornamental/vines/mandevilla/mandevilla-plant.htm