I'm sorry. We have been there, done that. I swear these skids take everything BM says, even with proof to the contrary, as fact as if it were a Bible. I have no idea how it happens and how it sticks but it is so damn annoying. And the worst part is, when you try to provide proof and show the truth, the kids get soooo defensive of their BMs. It's sad really.

We went through the same thing when our DD was born last year... BM reared her ugly head with financial abuse, demanding money for everything under the sun and seeking tons of unnecessary medical care for SS, billing us our large portion of course. She even billed us half of $4 for Tylenol. It was insane. I swear, we were paying hundreds of dollars in medical bills every week for like 7 months for SS. And of course all these medical issues "appeared" a week after DD was born, and magically and mysteriously "resolved" months later without actual treatment, when BM realized DH wasn't playing ball. It was BM's last ditch effort since she knew DH wouldn't engage any other way but medical expenses were court ordered. And SS was weird as hell with DD for a long time, I'm sure due to BM's brainwashing. Now he's great with her because DD wore him down. But it's always interesting to see SS shift back to old ways, especially when SS is with BM for long periods of time. To this day, SS still hides in his room and whispers his spy report to BM and GF when they call during our visits. I hear bits and pieces through the wall/door about me, DD, my family, DH's family, etc... yet never about DH. And of course, these reports always paint us in a negative light. He never mentions the positive because he knows he can't. And when we call him on it, he accuses us of eavesdropping and gets aggressive and defensive, blaming us for his reporting. It is all beyond dysfunctional, but it is dysfunction that BM normalizes and encourages. 

You aren't going to be able to control SD. Whether SD does it intentionally or misunderstands or is brainwashed into spying, it's an invasion of privacy and can wreak havoc on your household. And if DH fights SD on it every time, he will further alienate her. And of course you have to worry about your own kids and raising them right despite their toxicity and their Mom's toxicity. It's a hard spot to be in. I have yet to find the right answer to this. For SS, I have learned to tell him nothing and to expect him to tell everything to BM. Sometimes its unavoidable if something happens in real time, in front of SS. I just have to know that BM will find out and judge away. My answer is that if I don't want him to know or see something, DD and I just aren't around during his visits. If we aren't home, he can't report on us. 

When it comes to PAS and the kids that fall for it, there is no winning. Everything you say will just get twisted. I wish I had a success story to tell you but the only thing I came to learn is the older my SS got the worse the PAS got and it ultimately broke any father child relationship that was there. 

I'm sorry that you have this stress at the end of your pregnancy. This is supposed to be a joyful time for your family, not drama. 

Bc they are negative and human nature is negative by default.   In Chef's case, his ex MIL, Battleaxe Galactica, told everyone she received zero child support from the Girhippo's father which was an abject lie. 

Chef believed this too even in the face of evidence to the contrary.   I talked to Chef's oldest half brother some time ago and he knew the Gir's dad and SM.  He stated that the Gir's SM had complained about high CS going to the original HCGUBM Matriarch, Battleaxe Galactica.

Chef chose to continue to believe his loon of an ex-MIL instead of his own brother!  And the cycle continues.   SD will be a mini me of the HCGUBM.

Is he dumping SD on you ?   DH should be home if SD is at your home .  He should be handling this.

((((HUGS)))))

The SpermClan thought the same as the Spermidiot added three younger also out of wedlock spawn by two other baby mamas over the years. CS just kept going up.  Most States use some variant of the Income Shares model which factors in the income of both bio parents and parenting time.  Adding additional dependant children to either side does not generally have significant impact as elder earlier relationship children generally maintain CS priority within the courts.  

Never forget, sugsequent children with a newer mate are not full sibs to a SKid and subsequent children have a non related parent to provide support.  

Spermidiot was sequentially nailed for more CS every time either we or he asked for a CS review.  All while my DW's income went through the roof and the Spermidiot's income stayed fairly stagnant. and his three younger spawn showed up over the years.  SS is an only child in our mariage and the eldest of 4 for the Spermidiot.  All 4 are adults now.  Our son is doing great, has served in the USAF for 12+ years and is intending to serve at least 20 and retire.  #2 is on the dole. #3 is in prison, #4 is not far behind his inmate immediately elder brother.

As CS went up, the manipulations became more complex.  Spermidiot was ordered to provide medical insurance for SS from day one. He never did.  After the last CS review raised CS from $133/mo to $785/mo, a hearing that the SpermClan avoided, Spermidiot ran from the Constable serving process notification for the CS hearing, he came screaming into court crying about the direct payroll withholding of CS that was taking his entire pay check, he could not feed his other kids, etc.... CS was reduced to $385/mo after two years at $785 due to his avoidance of repeated hearing summons.  After that hearing, a few months later he attempted to get CS reduced by finally providing medical insurance for SS.  The Judge reset the 2yrs of no CS review and denied the request for CS reduction due to providing insurance.  

You may be very disappointed at the outcome of a CS review upon the birth of your next joint child with SO.