If my "baby" wasn't a gigantic 19 year old right now, @confusedex2 , I would think that you're me...
Take it from someone who has been there and made the mistake of facilitating a relationship between my DS and his paternal family for 15 years... give an inch and they'll use it as a precedent. The stress of it, the watching of your child winding up confused and hurt (which only stresses you out more) and the inevitable smug condescension towards you by the parents of the "father" of your child just isn't worth it. My ex and I were almost 30 when our son was born and we were together at the time, and had been for almost 8 years. DS was also planned by us both, and took almost 5 years to conceive (second child infertility, I have a daughter from a prior relationship). He refused to tell his parents that I was pregnant, despite the fact that he was still living with them only 3 miles from where DD and I lived. At 6 months pregnant, his mother arrived to harangue me about how they wanted me to have an abortion ("but of course, it's your choice, 13") and how absolutely stressed out my ex was about the whole situation. What he hadn't told them was that I suffered a partial miscarriage of DS' twin at 9 weeks - which he was told about, afterwards, ,when he finally deigned to answer my call (I suspect he was fucking around on me even then, in hindsight), and that I was more than prepared to raise DS without him, because I knew that I could do it (having been a single parent to DD from the very start). When DS was born, I refused to have ex in the room - so his mother camped out in the waiting room and tried to force her way in to take photographs of DS when he was minutes old (she was told to leave the hospital by the excellent and ferocious midwives) - although I did allow my ex in to meet DS for a while. For the first 12 months, I refused to let them spend time alone with DS - and he wasn't even breastfed. I was guilt-tripped, but there was just a niggle of suspicion there that made me go "nope". They tried to hijack every single special event for themselves - DS' birthdays, Christmases, Easter... it became like a game in the end, because I had to find humour somewhere. But when they did spend time with DS, they didn't look after him - actually, they gave him a life-changing TBI when he was 6, which resulted in the hospital reporting them to the police and SS for child neglect. Ex and I split when DS was 4, and after that, I had little to no say as to who DS spent time with during the 18 hours a month access (ex's choice - in 19 years he has never put DS to bed, read him a story, soothed him when he had nightmares... the 18 hours were 9 hours every other Saturday - and he was dumped on either ex's mother, or his new wife). When I needed to register DS' birth at 3 days old because he needed to see a GP, who wouldn't see him until he was registered... ex refused to pick up any of my calls, so that he could be on our son's birth certificate - so consequently, he isn't, His father threatened to take me to court to rectify this, I said "great; not a problem with that..." - he said he'd look into it (because why should I do the legwork?) and I'm still waiting, DS was 2 at this point. I received £100 a month in maintenance (and ex has a well paid job, plus side hustles), all childcare expenses were on my shoulders, and I was primary carer 100% of the time. I literally stopped trying to talk my son into seeing them when he was 15 - he knew that he wasn't there because they wanted to spend time with him, he was there to make them look good and/or babysit his younger half-siblings and cousins as he's the oldest (well... the oldest that ex's parents know about).
DS is an adult now and has little to no relationship with any of them. They guilt trip him (or try to, he's more immune to it now he's older and his boundaries are strong!) him about the fact that he and his father aren't close ("well, Mum, we would be if he'd actually put some effort in when I was a kid," was his statement the other week when the festive season's guilting began via text...). They moan when he leaves their texts on read... for weeks. And he's seen them once in 7 months, He just has no interest because of the fact that they have done nothing but make him feel like he's some sort of charity case because I was already a single mother when he came along... I apparently have a golden cunt that entrapped my partner of almost 8 years into talking me into having his baby (I wasn't keen at the start...). But as his Mum, I carry, and always will do, that residual guilt for ignoring my gut instincts when it came to my ex's family. I have watched my son be hurt (emotionally and physically) repeatedly by them, been spoken to like I'm a piece of dirt beneath their shoes because their son was too much of a coward to tell them that I was pregnant, until they couldn't browbeat me into a termination, and I have literally had to advocate/stop contact for my son's mental welfare so many times that I stopped counting (which of course makes me even more of the devil incarnate...), Everything has to be on their terms - and when my son turned 16 and wanted to spend Saturdays with his mates... they threw their toys out of the pram about it. Didn't like it when I told them that their son and I had been fucking like bunnies at the age of 16, and could they please respect my son's need to be a teenager (not my finest moment but by that stage... well.)
Don't let them set the precedent for anything in your DC's life, OP. Seriously. Trust me, that way madness lies. They're not interested in your baby - just in hurting you. Which is despicable, and says more about them than it ever will you or your DC. 