I think I’ve talked about this before, but…

Starpike is definitely in the Dornish Marches. My thinking is that it’s somewhat to the east of Horn Hill, closer to the Prince’s Pass and Nightsong. Its proximity to HIghgarden would also explain the Peakes’ links to the Gardeners and their long-time prominence.
Whitegrove I think is on the far sice of the Mander, solely on the basis that I think the name is definitely a play on Goldengrove – and because the sheer geographic expanse between the hills of the Red Mountains to the northwestern borders of the Reach really suggests something of the Peake’s “overmighty” ambitions.
As for Dunstonbury, that’s a tricky one. Given that it was the seat of House Manderly, I’m going to say it was somewhere on the banks of the Mander, but that’s still a huge range of territory from the rivermouth west of Highgarden to Tumbleton. I am going to suggest, based on the Manderly/Peake feud and the Bracken/Blackwood feud, that it’s somewhere on the northern bank which would put them right across the river from Starpike…and I’m going to say it’s somewhere between where the Silverhill river flows into the Mander and where the Cockleswent and the Mander merge at Cider Hill.