do what i did.
1. no trash talking me or my spouse
2. i dont care if you like it or not i will allow my partener to punish my child if needed

you will respect my decisions as his parent and if you cant then you just wont see him until you can

My DD's biodad died when she was 5, and I have remarried. I understand your problem, but this must be addressed and not ignored. If you and DH agree that he can discipline your son, then you need to make it clear to your MIL that it is not her place to tell your DH what he can and can't do. Please do not ignore her when she has a fit. This is a very important boundary, and if you let it slide now you will have a DH who thinks you are not standing up for him, and he will resent it. It's a slippery slope. If the answer is not letting your son go to grandma's until it's worked out, so be it.

Well, as fabulous as it is for your ex MIL that she has her thoughts on how to parent YOUR child, at the end of the day, she only gets as much say as you decide - just like your husband. It is up to you to set the rules for ex MIL in support of your husband. Ignoring it is probably not going to work, from experience. Taking your son away from grandma is also probably not the best plan. But, setting up your expectations with the grandma and following through is important. I would make it clear to grandma that YOU are the parent. You decide how to raise your child, not her. It is unfortunate that her son is no longer with the family, but that it is important to your family to be a cohesive unit. In order for that to happen, everyone's roles are to be respected, and if they are not, then contact time will be limited to maintain cohesiveness as a whole.

My MIL spoils the dickens out of my SS. She tried to tell me what my place was. She stopped spending time with her SS because my husband wasn't having it. He made sure to explain the expectations to her. He told her what would happen if she didn't follow through. The consequence was that she would no longer get to be his after school care. It made it harder for us, but in the long run, it was more important to my husband to have his son respect me and behave properly. I support him in this. Now, she fully supports me because she's seen the change in my ss. He has manners, he behaves, and he is respectful. He's not perfect, just like any other kid, but he is a good kid with good character - not sneaky and manipulative to get what he wants. And, I'm happy in my relationship and my home because we get along and there is mutual respect between SS and me.

I know most stepparents believe the worse thing in the world is having to deal with bioparents. But nothing can be more difficult than an former MIL after your spouse (or former spouse) has died.

They believe they speak for their late child about how the grandkids should be raised but they still act like grandparents to the kids. It's the world's worst combination.

My DH is a widower and his former MIL drove us crazy. The sooner you can get her out of your life, the better. My skids had a far closer relationship with their grandma than they did their father and she interfered with everything. She spread lies and nasty rumors about me and turned my skids against me.

Set boundaries and limitations that are appropriate for a grandparent. Do not let her tell you how to parent your child. If she doesn't agree to this, I completely support cutting off contact. Do not let your son see his grandparent as a parent or someone he would listen to over you and his stepfather.

If you believe the grandma will poison your son against his stepfather, then do something about it now while your son is young. I would consider a stepparent adoption.

My children's father passed when DS was 3 and DD was 5. I have since remarried and I went thru the very same thing. My opinion -- it's not like my (now) DH is trying to replace my children's father. He pretty much IS their father, at least the only one they will ever know and remember.

My first DH's mother was the same way... and we did make it clear to her that this is the way it was. It wasn't easy and I'll tell you why: she always felt a "claim" to my children. At the point in time my first DH was (terminally) ill, she didn't want anything to do with helping to care for him. She only wanted to take care of the kids. Noble, but I needed help with HER SON also. In fact at one point she even approached me about obtaining guardianship of the kids for herself (um, NO).

I think a lot of it in my situation was she certainly didn't want someone attaining a "parental figure" status in my children's lives if it couldn't be her.

Honestly, if it was a divorce situation it may have been a little bit different, I don't know. But I can speak from experience that if my current DH is the only father figure my children will have, he has the right to discipline them as long as it is in line with what he and I have agreed to.

I'd be telling her 'I'm sorry for your/our loss MIL and I am sure that we can all help the kids to come to terms with how things are now.'
She's got some sort of resentment brought about by grief maybe? A mother never gets over losing a child no matter how old the child is. There's an expectation that our kids will outlive us!
I think I would be straight with her though, tell her that you understand her good intentions but it's time to move on.
Let her know that no one can ever replace her son and you will not let the kids forget who their bio dad is. Reiterate during the conversation that it's time to move forward. It's going to take time for her to accept another man in the kids' lives, it's hard to lose a child.