Clowns don't readily accept replacements if a mate dies so be ready for some bullying and possibly outright fights. It took my female gold stripe maroon nearly three months before she stopped trying to attack the smaller male on sight. Even now she barely tolerates him being in the same open tank as her. I had him in a large acclimation box in the same tank and she would charge at him every time she came out from behind a rock and saw him.
As for the lion.. Well.. it's a lionfish it will eat what ever fits in its mouth, or flash its spines if it feels threatened. If you have a particularly aggressive or territorial clown and the lion gets close the clown will try to defend it's territory. Or if you have a smaller clown that the lion can fit in its mouth, hosting in an anemone or not it's going to be dinner sooner or later. Depending on the lionfish you may consider moving him to his own tank with other less territorial tank mates in with him. Otherwise this may be an issue with him and clowns.