Here is the ONLY way to deal with a situation where you have irresponsible people living in the same areas as you:
Call your landlord.
Get him to kick out anyone that isn't on the lease.
Don't share food or food costs. Only provide for yourself.
Keep your own set of food-wares in your locked room. Use them, wash them, return them.
If things are truly bad, call the landlord if you see drugs. Take pictures and/or video. Most states will FORCE the landlord to start eviction proceedings immediately, I'm unsure of Texas law however. Call the local police department if the landlord is of no help.
Start looking for somewhere new to move into and ways to get out of the lease.