Need some help. My parents have a basic(no name brand & what came with the mobile home 10 yrs ago) two-handle tub/shower faucet in their master bath. I tried the sink and both the hot and cold works for that. The problem is that only the hot water works in the bathroom tub. There's absolutely NO cold water coming out at all, not even a drip. I don't know the cause or what to do as I'm not a fixer upper with plumbing. Any help/advice?

This would usually be caused by debris in the inlet but you get dips most of the time. The inlet is clogged or the stem is striped. Shut off the main and disassemble the stem after removing the handle. Soory, can't be more specific without a brand