My Kindle library is a testament to chaotic reading. I have Madison books scattered everywhere, read based on nothing but the cover and my mood that day. And I loved every single one. Did I sometimes get a spoiler for a previous book's baby or engagement? Yeah. But in romance, the HEA is a given anyway. The journey is the point, not the destination spoiler. Knowing two people end up together doesn't ruin seeing how they get there. So, if a spoiler for a previous book's outcome is your main fear, I'd relax. It's a romance novel; the spoiler is literally 'they fall in love and live happily ever after.' The fun is in the specific bumps along the road.
Just pick the couple that sounds most interesting to you. Romance is about the central pairing, first and foremost. The series order is mostly for Easter eggs and side characters. The main love story in any given book is always complete. I started with 'Only One Regret' because the blurb about second-chance romance hooked me. Loved it. Then I went back and read the others to learn about the brother and cousins mentioned. Worked perfectly for me.
The author occasionally mentions in Facebook posts or newsletters which book fits where for super fans asking. But she hasn't compiled it into one official document. The series guides are the official stance, and they work perfectly.