So you shouldn't necessarily expect that your ex will 'get what he deserves' in the immediate future. However, if we assume that he's eventually convicted, here's the document which judges refer to:
http://www.sentencing...inst-the%20person.pdf
(See page 17)
The sentences there refer to a first-time offender, convicted of a single offence after a trial. An early guilty plea can see a reduction in the sentence. (In the case of a custodial sentence that's usually by one third). Previous convictions (especially for violence) can push the sentencing range higher, as can multiple offences and aggravating factors (such as assault upon a minor).
Without knowing all of the details (such as the extent of the victims' injuries, whether your ex is pleading guilty or whether he's got any previous convictions) it's hard to guess at his sentence, but he might be facing a sentence of 6 to 12 months (of which half will actually be spent in prison).
Chris