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How old is the plant? Are the spotty leaves on old growth or new growth? Is it getting proper water, feed, light and temperatures? How big are the spots?

If they are in the same area, and everything else is the same, the one facing north might appreciate more sun. Mandevilla tolerate full sun, but do best with dappled sun or light shade from 12 noon to 5pm. A few yellow leaves at the bottom of the plant is normal.

If the mandevilla stem is dry and brittle, I would cut it back to the point where it seems to be flexible. Hopefully, it will resume growing. This link might answer more mandevilla questions: https://www.gardeningknowhow.com/ornamental/vines/mandevilla/mandevilla-plant.htm

Your peppers may have bacterial leaf spot. This link will take you to a group of articles on bls: http://www.google.com/cse?cx=012078378210706707791%3Af1h5n_k1r5e&ie=UTF-8&q=bacterial+leaf+spot&oq=bacterial+leaf+spot&gs_l=partner.3...80037.80037.0.81189.1.1.0.0.0.0.253.253.2-1.1.0.gsnos%2Cn%3D13..0.0.0..1ac.hKIbY0Qz4a4#gsc.tab=0&gsc.q=bacterial%20leaf%20spot&gsc.page=1

Hopefully, the following article will help answer your question about peppers not blooming: https://www.gardeningknowhow.com/edible/vegetables/pepper/pepper-blossoms-falling-off.htm

I suggest a well balanced fertilizer like 20-20-20 or 14-14-14. It is my opinion that "bloom booster" fertilizers, with an analysis of 15-30-15, or something similar, are too high in potassium, and in the long run, are harmful to the plant. If you were to ask 10 growers of mandevilla, you'd probably get 10 different answers. What works best for one doesn't always work best for another.

This link will take you to several articles about mandevilla: http://www.google.com/cse?cx=012078378210706707791%3Af1h5n_k1r5e&ie=UTF-8&q=mandevillea#gsc.tab=0&gsc.q=mandevillea&gsc.page=1

Yes, and this article will help: https://www.gardeningknowhow.com/ornamental/vines/mandevilla/mandevilla-propagation.htm