Northern Balcony Lights

About 15⁰C is about the coolest you ant them to get.

Not much you can do, this is one of the outcomes when growing autos outdoors....tiny plants flowering. Next time grow photoperiod fems and in the same amount of time, you can harvest so much more. If space is an issue, plant the fems late in the season, 4-6 weeks before the summer solstice and the will stay smaller, but out yield any auto on the market when grown outdoors. Still not to late to put some new seeds in. When growing autos outdoors, planting about 4 weeks before the summer solstice will give better results, as the days are the longest they will be all year and then they will out perform any auto planted early in the season.

swollen female calyx

This is really only a concern during late flower when buds start getting dense. If you're unable to move them or put up a small temporary structure like a little hoop house then do your best to shake off the plants afterwards to remove as much rain as you can. I would avoid coverings that directly touch your plants, like trash bags, as you're likely to trap moisture against the buds and create the mold you're trying to prevent.