A lot of SKs feel that if they have positive feelings toward their stepmom, its a betrayal of their mom.  Its called a loyalty bond and I bet that's whats happening to you.  I can tell you're hurt but I hope you can absorb this dynamic and realize its not your fault and actually not the kids' fault, either.  It's just human emotions.

In some cases, the BM enforces this feeling but I bet it occurs even when the BMs don't encourage it.

Good luck,  step-parenting is an intense, complicated situation.  Lots of strong emotion.

Kids complain about parents - both bio and step. It's part of the teen years. The chaffing against rules. The wanting to hurry up and be an adult. 

My bigger issue here is why the adults are running to you with this? If they actually thought Dad was a problem, they should have been talking to Dad. A problem that you cook too much. Kids want junk food, so are you supposed to stop cooking and order take out for them. These adults are nuts. At this point I'd be telling them that if they are concerned there is abuse they should be calling children's services. Otherwise they need to tell the kids to advocate for themself. 

Make no mistake.  Busybodies are anything but well meaning.  Love is not a feeling. It is action. If anyone is professing love but backstabbing, they do not love you.  So, Keep It Stupid Simple. KISS

Gauge people by their actions not their words. What you want  them to feel is irrelevant.  How they feel is even less relevant.  What they do is all that is relevant.

Kids do not get consideration based on their wants and likes. The only consideration minor children get is based on their needs as decided by the adults. So, stop giving a shit about their feels, their desires, their wants, their likes.  Those things become their choice when they reach the age of majority.  If they are not earning consideration of their wants and likes with absolute lock step alignment with reasonable behavior, they get no consideration.

Since they are clearly playing the manipulative bullshit games, set and enforce the standards of behavior and standards of performance that you require and implement a firm accountability system to deliver escalating abject misery inducing consequences if they make the mistake of failing to deliver the the standards set by the adults. If your SO does not have the testicular fortitude to stand firm on standards and consequences, then the SO gets no say.

Take care of you.  Focus on living your best life.

Good luck.

I cook and do, because I want to. I enjoy doing the holidays.  I enjoy haveing people over .  I don't do it for the SK.  Cooking just gets you in the holiday mood .  This is something I don't want to loose. I be the first to day Happy Holidays 

First, it's possible for kids to love their parents/like their step parents... and still complain or not love everything their parents do. They can do it for a variety of reasons... to be cool in front of friends.. to try to get a message back to a parent without direct confrontation... to gain sympathy from someone.. or just because they woke up on the wrong side of the bed.  

That being said... I think you may be trying to read too much into things.  

In the first example.. where the relative was relaying their frustration with DAD.. it was the "well meaning" relative that tried to make it about YOU.. not your DH... so it doesn't seem it's the kids complaining.. more the relative making some assumptions.  I would be cautious around that relative TBH... they are not your ally in any way.

Re the issue about you getting stressed over hosting.. could it have been more of a.. "gosh, wish she didn't get so stressed.. if she doesn't want to do it.. just don't".. it doesn't mean they don't like you.. or appreciate your efforts, but being in a house with someone getting really stressed can be uncomfortable for everyone.. and I think they are maybe saying.. that they would be ok if you weren't killing yourself to do this stuff. 

I am also going to weigh in on the people telling you "they are dad's problem".. to me, that sounds like they are trying to respond to your complaints about the kids... that you should not have to take on the kid problems.. they are dad's kids.. not yours.. let him deal with them.  That, again.. is not the kids talking behind your back.. sounds more like the opposite.

The lunch issue?  Maybe at their age.. "buying lunch" is the cool thing to do.. they don't know how to tell you that without hurting your feelings.. so they do an end run to a relative. 

I think people are generally trying to tell you to be a little less invested in a parental role for these kids that are becoming and are teens.  If they don't want your to make lunch.. let dad give them money to buy it.  Instead of killing yourself for some birthday party for them..let dad decide what he wants... 

In the end, I don't think the kids dislike you necessarily.. and I don't think they are truly talking badly behind your back.. but they are not mature and have a hard time likely going to someone to present their case on something.. so they use their relatives to broach subjects.. especialy when they know it might hurt someone's feelings.. and you do seem to be sensitive to these issues.  

There is nothing wrong with wanting to do things nicely... but if the tension in the house gets too high because you are at your limit.. and maybe snapping at people.. or showing a lot of stress.. they maybe would rather be in a calm house than have the fancy spread of food.  Since you are now aware it is potentially bothering them.. maybe you can be more self aware around those issues.. and not let it get to that level.

I mean.. the kids, should obviously be respectful to you.. and maybe part of that for them is they don't feel they can complain to you or dad about lunches.. but, I don't know that this is some sign of high dysfunction on their part.. kids... especially teens.. are learning how to navigate confrontations and discussions.. and they are also prone to not liking or being embarassed by parents too.. so it may not be as personal as you are taking it now.

I don't know, I think some of this is normal.  I used to  complain about my parents as a kid and I'm sure my bios complain about me and my husband (their bio father).  I still complain about my mom at times. My dad passed away in 2001 or i would probably complain about something he was doing.  Now I complain about him not being here.   Sure, some of it could be a loyalty bind but kids complain about their bio parents.  What isn't normal is the busybodies coming to you with the complaints.  If it's a real problem, then sure, they can come to you and your husband.  The complaints you've mentioned are not worth the busybodies wasting your time and theirs, and they need to mind their own business.