It sounds to me as if you're unhappy being in the band and would prefer to focus on your solo thing?

Or that you'd rather do the lead vocals?

If that's the case and you're sure, then just take your shot. There's no good way of telling somebody it isn't working that they'll be happy with. Especially when egos are involved. But obviously be prepared for the consequences. If he leaves, then the songs he's written are gone.

Being a front man is a hard gig. Especially at the amateur level where the crowds are small and mostly composed of friends/family. If he's struggling in that department you also could get him to watch good frontmen on youtube to see what they do and try to pick up some tricks.

As for vocals, there's no shortcuts to being good, you need to just keep practising.

Also beware of family and friends feedback to a certain degree, unless you trust their musical opinions enough to have them in your band. They may be trying to give you feedback they think you want to hear!

A few eminem albums end with a track where he literally says thank you for coming, hope you enjoyed the show.

Examples I can think of are at the end of "Untitled" from the recovery album and "Encore/Curtains down" from encore where the crowd are calling his name for an encore and he comes back out and starts shooting with a gun.