What's your question? Ask

Mandevilla can be propagated by layering or dividing the root-ball; however, most new plants are produced from softwood cuttings taken in early spring. For more information on cuttings, check out these articles: https://www.gardeningknowhow.com/ornamental/trees/tgen/how-to-root-cuttings-from-various-shrubs-bushes-and-trees.htm
https://www.gardeningknowhow.com/special/children/mandevilla-propagation.htm

Perhaps too much. It does not like to be soggy. Ensure you have fast-draining soil. After watering the plant thoroughly, do not water again until the soil is almost dried out. Make sure the sun exposure is not too intense.

No you would need to bring indoors if temperatures drop below 5o degrees.

Here is a link with more information.

https://www.gardeningknowhow.com/ornamental/vines/mandevilla/mandevilla-plant.htm

You have a Mandevilla Plant.

Here is a link to help you.

https://www.gardeningknowhow.com/ornamental/vines/mandevilla/mandevilla-plant.htm

It sounds as if your plant may be watered too much. I would suggest you remove the yellow leaves and then check the soil around the plant every two or three days to see if it is too moist or too dry. If the soil still is moist when you insert one fingertip into it, your plant will not need water for three or four days. Even then, water it just enough to moisten the soil and see if the leaves stop turning yellow. One thing about Mandevilla vines is that they should be trimmed and bit and brought indoors for the winter because they cannot withstand temperatures below 60 degrees. With good care and enough indoor light, your plant should survive indoors and be ready to put outside next spring when night-time temperatures are above 60 degrees.

Did anybody water them while you were away? It sounds as if the plants have dried out and are in dire need of water. Plants in containers require more watering than those in the ground--once a day and twice daily in temps over 85 F.

If the stems are brown and brittle, then they are dead and it would be best to cut them back to wherever you see green wood. You should also soak the containers in water for about 5-10 min. to rehydrate the plants. Hopefully, they will bounce back.