if interference is detecting an inteference but you can't combine
i would recommend doing import diagnostics on all your parts (with no features) to make sure there aren't bad models
then i would make sure everything survives ctrl-q to make sure the geometry is solid
but the answer is if there are interferences, you probably wont' get a good mesh even if it would let you get past this
Ok. Thank you, I finally used the cavity feature one by one but I'll try what you've said too.