At the end of the day, you will need to start by defining exactly the
set of equations you want to solve. This is not clear to me from your
post above, but once you have the equations that describe your model,
you can start thinking about how to implement them.
There are numerous questions and answers on this forum regarding
fluid-structure interaction problems. You might also want to look
through the list of publications at
https://dealii.org/community/publications/
to see what others have done and how they have done that.
Best
W.