Jake Paul is the king of fake-outs, which is why we question his engagement to Tana Mongeau in the first place (btw, 90% of you think their engagement is fake, according to our poll) ... and NOW we're questioning his Caci Twins' claim that they found a pregnancy test in his bathroom!

When we caught up with Jake and Tana last night at Craig's, we asked the newly-engaged couple if she's pregnant with twins because ... why not? The Caci Twins say Tana's trying to hide her pregnancy from Jake because why -- she wanted to make sure he was marrying her for love and not for paternity?

Anyway ... roll tape!