What was the relation between Prophet Ismail (A.S) and Prophet Ishaq (A.S)?

Ismael was the first son of Abraham , probably genetically speaking median is the second one and ishag was the third.
God need to be fair and as it seems to me he promised Hager to have born to a father of 12 trips kings.
so who it came that ishag was blessed by god and the land promised to his father turned to a god promise to his third son excluding the the others?
Ismaels and Medians offspring continued for several thousand of years in the land of Canaan and around it,while the Israelite fled out of it due to famine to Eyjept and scattered due to invasion of Babylonians.
is it real;y accepted for those who fled to have extra wright over those how struggle and insist in keeping their relation with the land over thousand of year?