My mother_ often clothes on Sunday(wash ,washes,has washed ,

应该是My mother often washes clothes on Sunday. often表示经常,所以用一般现在时.
It has snowed for two days, and the roads will be blocked if it won't stop soon.
这里有has,你就不能再用is了,动词只有一个.这是一个时态混合的句子,前半句是现在完成时,表示过去的情况影响到了现在,说明雪还没有停. 后半句是意思是如果雪不停的话,道路将被封堵.是将来时.