Hi fellow bike builders

In the future, I hope to start designing tandem bikes with threaded couplers. PArt of me is worried that if I try to design a bike for more than two people, the frame may start to bend in the middle. I am wondering if anyone here has tried to use Bikecads ability to export to freecad to import a model of their bike into a dedicated mechanical engineering software like fusion360 or solidworks. I am also wondering if I am just being paranoid, but it seems to me that the longer the bike the greater the likelihood that structural issues will occur, especially if one desires to add hinges or couplings to help make the bike easier to transport.

Thanks for the help