He wrote few letters to any of his family ,but he sent a few

这句话的问题应该不在some或者any上面吧。我猜是要辨析few和a few 的用法。。few表否定,前半句是说“他没怎么给家里写信”；a few 表肯定,所以后半句是说“但是他给朋友寄了很多卡片”。some 跟any 也是根据这个来的,any 用在否定句中,前半句是用few否定,所以是用any,而some是用在肯定句中。