It sounds like your outdoor furniture faced moisture issues, which can lead to rot, especially with untreated wood. Stud grade lumber, like 2x4s and 1x2s, is not ideal for outdoor use, as it's typically not treated to withstand the elements.
For outdoor furniture, using pressure-treated wood is a good choice since it's treated to resist rot and insects. Make sure to let it dry out after treatment; this can take a few weeks. Once it's dry, apply a high-quality exterior stain or sealant designed for outdoor use. Look for products that offer UV protection and water resistance, such as those made by brands like Behr or Cabot. Prices for quality exterior stains typically range from $30 to $60 per gallon, depending on the brand and finish.
In addition, consider using a wood preservative before staining, as this can further protect the wood from moisture damage.
As a next step, I recommend getting 2-3 local quotes on Handyman.com for a professional assessment or help with your outdoor furniture project.
— Assisted answer