You can also gain both their support under specific circumstances.
- Wreave must be alive instead of Wrex.
- You had to destroy Maelon's data in ME2.
With Maelon's data destroyed Eve dies during the run towards the genophage distribution facility, you can then persuade Mordin that with Eve dead Wreave will have no one to control his krogan behavior and he will agree on faking the genophage cure. Wreave thinks he's cured, you get Krogan support. You didn't cure the genophage, you get Salarian support.
If Wrex is alive, the only way is by saving the council dude.
Either way is pretty heartbreaking, You either lose Wrex or you lose Thane or Kirrahe.