we want to sit down and to relax.这个句子有错吗,to relax是不是能理解为并列宾语

有错,动词不定式两个连用时,第二个一般省去TO,即
We want to sit down and relax.（动词不定式作宾语）
或
we want to sit down to relax（TO RELAX 动词不定式作目的状语）