It could be one of the viral diseases or root problems but may have just been setback by the cold wet winter you had in Cali. Papaya are easy to grow plants and if they have problems it may be best to replace them. Your trees look like they are about 3 feet tall and from seed could be replaced in a few months. You don't mention the variety so I assume you grew from a seed out of a bought papaya. Be aware that some commercial growers use hybrid F1 seeds which may not breed true. I've had great success with this vendor's disease resistant seed with 100% useful female or hermaphrodite plants and not a single male in my planting. If you choose one of these varieties you can plant a single plant and not have to select out males. If you want to get serious about papaya check them out.
https://www.alohaseed.com/index.htmMy best advice is that papaya is a demanding plant that is very greedy because of it's high growth rate and heavy fruit production for size, up to 200 lbs of fruit on a single stem. They need the most fertile conditions possible with no setbacks from weather or shortages of water and nutrition. By growing single plants they grow stouter and straighter trunks instead of leaning and are therefore less likely to topple. I've had good luck transplanting them deeper than in seedling pots, burying up to 1/2 the trunk, roots form adventitiously along the stem for better stabilization. Lastly they are susceptible to root rots so planting on a dry spot or mound helps avoid that.
