generally, yes...since writing will be your bread and butter. for social sciences you need to be decent at statistics too but you can't escape writing since your assignments will mostly be writing academic papers. and take note, academic writing is very different from your normal everyday kind of writing.

the way you type..i think you should think twice before going into humanities or social sciences.

i don't think profs will penalise grammar mistakes per se but it's almost a given that you shouldn't be making grammar mistakes...if your language standard is so bad that you're making frequent glaring basic errors it'll just make you look bad and lower their general impression of you. no one likes reading a paper written in horrible english.