Faction Heir selection

[Yoko Kono]

Is there any way to influence this
In my current Scotland campaign my king had four sons before dieing in 1128
His eldest son, edward, becomes king
1148 and the new king is killed in fighting as york is sacked by backstabbing english
His brother, edmund the 2nd born, is also killed as wales too is taken the same year
this left two sons of which the youngest, david becomes king
1156 and king david is killed leading a successful assault on york with limited resources
the remaining 3rd born (alexander i think) becomes king and within two turns has adopted two sons just one and two years his junior
he then adopts another son (his grandson) to his youngest adopted son
but now edmund (the second born killed in 1148) has a son come of age
also david (king killed in 1156) has a son ready to mature
the thing is the heir is set to be the first adopted son of alexander but i think it really should be a canmore (the original kings family name) of pure blood
i want to keep the canmores legacy going and prevent iit going to some adopted son ( i feel like the english have imposed these sons upon me even tho i needed the generals at the time)
how do i ensure that when alexander dies (he is 40 and his two "sons" are 39 and 38 while his "grandson" is 37) the canmore sons of david or edmund will take the throne?

EDIT: current king has two canmore daughters but only adopted sons