What's going to happen to his bar card, will it be investigated independently or wait for police outcome before hearing any complaint?
While they could independently start an investigation even before a conviction (or even if charges are dismissed), generally something like a felony concivction automatically triggers one. I'm not sure if it's mandatory, but sometimes it's an immediate suspension pending review, but sometimes they'll let the lawyer wind down his practice in an orderly fashion and transfer ongoing cases.
Since Nick is non-practicing, there really would be no urgency one way or the other, so if it's automatic they'll just suspend him on the spot, but if not, there's no real rush like there would be if a lawyer was so out of hand he was actively fucking up cases.
They're generally pretty lenient about drug stuff. There might be a short suspension for mere possession (dealing would be a far more serious issue), with screening for substance abuse problems, and maybe conditions to get reinstated like attending a Bar-approved rehab and/or returning to practice on a probationary basis, supervised by another lawyer (sometimes also a recovering addict and I've seen that even be someone like an AA/NA sponsor).
The guns thing makes it a bit more serious but technical violations of possession laws are really not generally considered a crime of moral turpitude, much like drugs. The combination looks worse but I don't see it appreciably worsening his situation.
The wild card is the child abuse/neglect part of it, because that clearly reflects very poorly on Nick's (lack of) moral character and could very easily be considered the sort of crime of moral turpitude that warrants harsher sanctions.
tl;dr if he just cops a plea on drugs and/or guns he's probably ultimately okay (assuming he even wants to get his license back) but the child-related charges could be a doozy if he's convicted of those, or theoretically, even if he isn't. Without the child-related charges, he probably cops a brief suspension at worst and possibly even something as mild as a non-public reprimand.
ATP, this mess rests solely at the feet of Nick. He invited this woman into his family and submitted to her invading his family, and is probably trying to contain her.
It takes two to neglect a child. Both parents share the responsibility and the blame when their kids are stinking, starving and filthy in unwashed clothes. They are both equally reprehensible in their criminal abuse and neglect of their own children.
He's gonna be in for a rude shock when the money is all gone, and he's bald, and ugly as fuck, and even low IQ golddigging BPD Minnesota 6s won't throw themselves at him anymore.
This skeletal faggot already looks like an "After" picture in a Faces of Meth montage.