If your brothers don't physically harm you and their only problem is being slightly vicious then you shouldn't worry much about hanging out with them while you can still spiritually protect yourself from negative energies that may by released by them.
You can take a simple cloth or a red ribbon and include protective herbs / stones /ingredients when you make a sort of protective symbol. You may use the following:
*Obsidian - this stone is considered to be a very protective stone which also happens to be a grounding stone. It can be a very great addition to the bag you're going to make. This is good since it's going to banish and back of any negative energy that floats around or is sent in a specific moment.
*Snowflake is as far as I know a stone which holds the property of protecting women specifically. Adding this stone to the little bag you're going to make is very recommended so you should do it. It will add a lot to what you're going to do and I specifically recommend using this stone. On a side note you can also do something to mix and add the iron and the obsidian together in some way by placing it into a proper place which is appropriate.
*Iron- I recommend adding some iron because it's considered to be
protective. I am also into Astrology and I can tell you that this stone is related with the planet Mars which can be an advantage for you if astrology represents something which is more that merely symbolic. In case iron is a though thing to work with for you, you may use some gemstones that contain irons and are good for protections such as:
BllodStone, Hematite, Tiger Eye, etc... These gemstones are very
recommended to be added to what you're going to make while the also contain iron which, as I said is very recommended as a protective item !
*Any specific sigils or protective symbols you may find- runes, sigils, symbols are really recommended to carve on something while dealing with protective work. I specifically recommend you carving some runes especially the rune Tiwaz (Tyr). Something better that I've heard of is anticlockwise spirals which is very neat as a use of protective rune and symbol.
On a side note you can either make a small bag with a red ribbon and either make an amulet which may be less comfortable. Let her carry this in special events...