Answer: It probably isn't too late to pick the lemons and juice them, but you may find the avocados are damaged beyond repair, especially if they spent more than an hour or two in frosty weather. Why not pick one or two and take them indoors to see if they ripen without mushy flesh. If so, pick the rest; if not, either wait for the avocados to drop on their own, or harvest and destroy.
This unusual cold snap has taken quite a toll on nearly everyone's plants so you're not alone. Best wishes with your garden!
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