I don't understand why "nós queimam" is acceptable. Shouldn't it be "eles quiemam"?
yes!, and in the past tense "eles queimaram".
past is expressed with the present tense, is that normal ?
some verbs are the same for present and past when conjugated for nós. Nós queimamos = we burn/burnt. Nós corremos = we run/ran. Nós lemos = we read/read(past). Nós comemos = we eat/ate.