What you'll want to do is implement a driver, and have a base class, then add either a FocusInterface or the filterwheel stuff, which looks to be under FilterInterface (I haven't dealt with that.)
The ---Interface ones can be added on to another base class.
For examples (there are more)
lx200_OnStep (which does the Focuser (via lx200), Weather, Rotator, and I think something else in addition to the base lx200(Telescope) class.)
TeenAstro (which was a fork of OnStep at one point.) Which does the focuser separately, and I think passes it through? It might use a separate USB. Not 100% sure.
Also the base lx200 which can do a FocusInterface on top of telescope.
Several of the things in focuser also do a rotatorinterface, and I think the Pegasus does as well.
I don't think there are any device examples using FilterInterface per this,
www.indilib.org/api/classINDI_1_1FilterInterface.html So you might make the base class FilterWheel and use the FocuserInterface if you want examples to work from.