I used to get it from SIL who lived in MN - many many states away. She came to visit last summer and got to see first hand some of SS8 behaviour (he threw a fit on the living room floor for almost two hours because he refused to eat dinner and we wouldn't give him dessert) and I haven't heard from her since - LoL. She was going by what BM told her - they are besties the way it sounds. 

SIL is weirdly cold to me... I kind of just ignore it... I'm fiarly certain it's because I put my foot down and told DH we don't have the rexources or time to be going to grab my neice and nephew every day... And since they refuse to contribute to snacks or juices, or food that their kids much through, we cna't afford to be picking them up all the time and giving it to them when we're not doing awesome financially... DH and I basically ended up deciding that if we could afford to fee two extra kids (that are blackholes and don't have rules) then we'd be spending it on our own place instead of them... Also that it's not our fault BIL and SIL refuse to arrange their schedules for their kids and BOTH decided they wanted not kid friendly jobs and then they picked a daycare that closes 3 hours before they get off... Just because they made that choice, doesn't mean we can afford to support two extra kids...

Since then we've still been struggling financially, but we're not completely broke a week into payday and can actually make it to the next one. So SIL is cold, but it was the best thing for us.

You're not being too hard on the skid, some people just get sensitive over weird things and decide that you (probably as the newcomer compared to everyone else) must be the issue... My SIL has been with BIl for like 14 years (somewhere in junior high...) so therfore as someone who's only been around a few years, any issues she has, it makes it eaier for her to rationalize blaming me. FUnny thing is she hated the ex too, wouldn't even talk to her, so I still haven't really found logic behind it... So I'd just ignore them and keep doing you. You don't owe them an explination. Make sure your DH has your back.

My SIL , Thank God, lived states away, pulled crap all the time.  She would send bday cards and gifts to skids but never mine.  Told me I needed to just back off after ss was arrested for drag racing and wrecking a friends car.  Thank you notes for gifts we sent were only addressed and sent to my DH.  She hugged my Dh's ex wife like a long lost friend for 5 minutes at a wedding right in front of me even though they haven't seen each other in more than 15 years.  So yeah,  I totally get it.  I went low contact and that has helped a ton.  What goes on in your family is absolutely none of her business to comment on,  She's instigating problems where there are none.  She is not the niece and needed police!

KMommy,
 If your  sister in laws don't pay your bills or put a roof over your head than to h@ll with what they say or think. I'd block them too. Life is short to be stressed out by people who have no clue what goes on in YOUR HOME. I'd shut this down very quickly and tell them to mind their business. The kids are well, healthy, and taken cared of. They can tend to their own issues and mind yours. Don't entertain their antics it only gives them fuel to do it even more. I have no problem cutting people off, inlaws or not. If they don't add positivity to your life then f@ck em'.

My DH's parents are deceased and I pretty much ignore the rest of his family. DH prefers to "love them from afar", as he puts it, so it makes it easy.

Having reasonable, age appropriate expectations for kids, ANY kids, is not being hard on them, it's simply teaching them how to act, how to be decent human beings. How dare you!

How old is your SS?

Why tolerate it or stand there trying to defend yourself? 

You need to straight up inform them that if they have issues with the way you try and parent SS that they can tell their son/brother to get off his *ss and parent his own kid. When you are running around caring for and chasing three kids under the age of two while your DH his his head in a video game , the last thing you need and/or want is their two cents.

There is nothing wrong with expecting a six yr old to have been raised by his father to use manners and to respect other people's (his little brothers) property. But his father doesn't help with nor parent any of his kids, so it's all on you. Three of those children belong to you, four of these children (aka all of them ) belong to your husband. 

If they can not respect you and your parenting in your home, they can stay away. If you are visiting over at one of their homes, stop doing so. You have your hands full enough without the frustration they cause you. Maybe your SIL would like to come wipe the 6yr old's *ss everytime his father refuses to either teach him or do it himself.

That sounds like a damned if you do, damned if you don't situation.  I'll bet if you hadn't corrected SS the 3 year old's mom would have complained that you were allowing SS to bully/hurt her child.  Where was your husband for this?  Does he have your back?

Tell them all to STFU and block their sorry asses.  Why associate with aholes? There are so many lovely people in the world.  Don’t waste time on the negative nellies of the world.