C.S.
Do you have a bath ring for him to sit in? If not I'd try that for the standing up. If that doesn't work just take him out of the tub and tell him why he has to get out early.
As far as his face in the water, I wouldn't even worry about that. As long as you stay right by his side he's not going to drown. My kids did it when they were that age and grew out of it by about 15 months.