1 这个句子的主语是单数,所以空格应该填is playing.
因为这个句子的失态是现在进行时（后面有now这个时间状语）,所以要用be doing这种形式
2 如果是and,2个人是并列关系,主语就是复数了
with的话就是一个状语而已,看with前面的主语是单数还是复数而定
举例子来说,这句话的正常语序应该是
she is playing games with her brother now.(单数)
she and her brother are playing games now.(复数)
they with their mom are playing games now(复数)主语是they