Bora-Care should only be applied to raw wood. It will not penetrate through any wood that has been pre-treated. Polyurethane is equivalent to applying paint, so the best process would indeed to be strip the finish and apply Boracare as this is the only product that will penetrate through the wood and eliminate the existing infestation and prevent future infestations.
You could use a product called Boracare on the barrels but you would be required to seal the inside of the wine barrel after application. The red/white wine stain will not affect the application, only if it were stained with an actual wood stain or sealant.
Bora-Care will penetrate through the wood and kill any insect eating the wood no matter where they are in the wood. However, it can only be applied to raw wood so you would need to apply it to the side that is not painted. It cannot be applied to wood that is painted, stained, or sealed. If your wood is painted, stained, or sealed, then you will need to drill holes and inject Bora-Care or sand the finish off of the wood, treat with Bora-Care, and then refinish the wood
Yes, you can apply paint or stain (oil or water based) to the wood 48 hours after it has been treated with Bora-Care.
Bora-Care is meant to be applied on all surfaces of raw, unfinished wood so it penetrates all the way to the center of the wood, and will last the lifetime of the wood.
Boracare should only be applied directly to wood. We would recommend using something like Termidor Foam in the wall voids. This product will be injected at the studs of the wall. Termidor Foam is a non-repellent so the termites do not know they are coming in contact with it. You can drill holes in the stud every 10-12 inches apart. This product has a residual of 3 months.
Bora-Care is a very safe product and it is considered a green product as well. Typically, it takes about an hour for the surface of the wood to dry. After application has dried completely, it should be perfectly fine for children and pets to re-enter the house. Please read the BoraCare product label for complete usage instructions. Boracare does have to be applied to raw, untreated, unpainted wood.