100% take it further, some form of intervention is an absolute must, it doesn't matter whether your fears are grounded your father needs to be accused sooner rather than later and it is most important that this is tackled with every family member present.
Do not give any advanced warning regarding what you want to discuss, just get everybody in a room together, (better if it is in a public space as neutral ground is preferable) and get your concerns out in the open.
It is almost certainly better if everyone is relaxed too so a few rounds of drinks will help smooth the process through.
Good luck mate, we're all rooting for you.