The reading for this word is quite strange. If you know 二つ's reading, you can use that to remember the 二 part (ふた). But, the り that is the 人 is a total exception, something you won't see too often (though you may have seen it in 一人). If you can use the reading of 一人 (aka if you've learned it already) then definitely use that. If not, do your best to remember the reading on your own. It's a strange one that doesn't connect to much else.