capital gains tax on 2-family house

[Jasmine Zhang]

Hello, I live in 2-family house, I live on the first floor and rent out the second floor. I am wondering if for the 2 of the 5 years before the sale, I use both units for myself (e.g. I can have parents visiting me and living on 2FL) or leave it empty, would I be able to exclude all the profit from capital gains tax if it's within the limit (250,000)? 

Any CPA or lawyer can enlighten me or anybody having similar experience? I really appreciate you sharing your expertise!