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They can take it getting pretty cold. Normally, around 28F without any damage. This article will help:
https://www.gardeningknowhow.com/edible/vegetables/peas/how-low-of-a-temperature-can-peas-stand.htm

This article will help you with that:
https://www.gardeningknowhow.com/edible/vegetables/onion/find-how-to-grow-onions-in-your-garden.htm

As long as it's only a mild frost, they should be fine. Here is an article that you may find helpful: https://www.gardeningknowhow.com/plant-problems/environmental/frost-how-to-protect-your-plants.htm

This article will help you:
https://www.gardeningknowhow.com/edible/vegetables/onion/growing-onion-seed.htm

Fertilizer while the sets are young can burn them. Give them a little time to establish and then you can fertilize with a slightly phosphorous heavy fertilizer. Before fertilizing, make sure the plants are well watered and try to fertilize on a cloudy day. This will reduce the risk of burning the plants.

They may produce bulbs this year, but it may be iffy. The same lack that caused them not to produce last year likely still a factor. Try adding some bone meal to the soil to help with bulb production.