My experience might help you a bit. I felt similarly to you about family helping out with childcare when I went back to work, I was very nervous about as we'd found a great childminder who knew exactly what she was doing and who I felt I could trust. But then my DM and MIL both wanted to have our DS for a few days in the week meaning that we only needed the childminder for 2 days rather than 5.
My DM is one of those people who rushes about all day, I was worried about routine and naps. She was also quite slack on what I thought were safety issues, for instance, as DS got older he'd be crawling about on the floor and she'd be sitting in the sofa, I was worried he'd put something in his mouth or fall over when pulling himself up. Looking back, they were legitimate worries at the time but were actually unnecessary.
My MIL seemed completely unresponsive to DS, she didn't seem to know what on earth to do with him. He's be crying and, like yours, she'd cradle him when I'd already explained that this made him worse. She'd be completely unstimulating for him, I was worried he'd be bored and that going from the chaos with one person to the boredom with another would be disruptive. But my DH really insisted that we try it, and so we did.
I was completely wrong about the effects of both situations - DS loves being with his grandparents and has an amazing relationship with both of them. With MIL she just needed time on her own with him to figure out what to do with him, my constant presence was off putting and she didn't feel able to try things when I was there. She has an amazing, calming effect on DS and has taught him so many things that I probably couldn't have done at this stage or that the childminder wouldn't have time to do with the other children she has to look after.
Similarly, he loves the business of being with my DM, she takes him to different places and he knows how he has to behave whilst she is out with him. He doesn't need reigns or a stroller when he's out with her as he holds hands, gives him jobs to do and keeps him entertained. Now obviously these are things I try with him too and that the childminder tries too, but when it's just DS and DM she can really focus on him. The frequency I have the chance to do this because of work, or the chances the CM gets because she has other children, are very few.
This has turned into a long post, sorry. My point is that I really think you should give family a chance to look after your baby. They might do things differently but that can lead to a more balanced and happier child. It will strengthen their bond and if you know there aren't any really dangerous reasons as to why they shouldn't help out then it's definitely worth trying. After a few months, if things don't seem to work out then you can always change plans. You've already said that they take holidays etc so if you can cover these then see now it goes. I'm happy I didn't just rely on a nursery or CM, not that I wasn't happy with the settings, but because it's nice to see that DS has bonded with family.
Try not to worry OP, it's hard returning to work but it does get easier and the worrying reduces somewhat, eventually.