回答1.those指代人,故关系代词用who
2.rather than可以连接两个动词、两个不定式、两个动名词、两个介词短语等：
We will have the meeting in the classroom rather than in the great hall.
She enjoys singing rather than dancing.
I decided to write rather than (to) telephone.
He ran rather than walked.
回到问题2：R.Quirk编著的《英语语法大全》p.1387明确指出：和as well as及in stead of一样,rather than后面跟一个和主句中的动词形式并不匹配的ing分词分句时,它是介词,而不是准并列连词：
Their actions precipitated the war rather than averting it.
他们的行为促使战争爆发而不是避免战争.
故句中用focusing是把rather than 作为介词来用了.当然,若把rather than 作为并列连词来用,这里用focus也对,.