How long does it take to adjust status through EB-5 from inside the U.S. for a family on different visas?

Assuming the Priority Date remains current then I would anticipate 12-18 months. Entering on a visitor visa for the purpose of adjusting status is a problem though, as a visitor is supposed to have an intent to return abroad and not immigrate.

You cannot file for adjustment in the week of his arrival as it would trigger misrepresentation upon entry. This would NOT be good for any of you. AOS applications tend to take 2+ years. 12mo minimum. But you may be able to push for quicker adjudication through the court system.

That plan would likely be considered visa fraud perpetrated by your dad so you should certainly seek advice from experienced immigration counsel before moving ahead with that plan.

If the visa is available, I would guess about 2 years for adjustment of status.