Brine is water over 50 ppt, so you will need roughly 2/3 cup of salt per gallon to reach a "brine" level.
I never bother with salt or boiling on any wood I have collected and used.
I've used oak,hawthorn, beech and apple.
You need to make sure the branches are completely dead and free from any sap or green wood.
I normally just give them a good scrub and poor boiling water from the kettle over them.
Pretty soaking will help to remove some of the tannins but the tannins can take a very long time to stop.
I've been doing this for years and never had any issues.