are all acid salts alkaline?

(1) Some acid salts are acidic. For example, the aqueous solutions of hydrogensulphate salts (e.g. NaHSO4) are acidic.

(2) Some acid salts are alkaline. For example, the aqueous solutions of hydrogencarbonate salts (e.g. NaHCO3) are alkaline.

Reason:
(1) Consider NaHSO4.
The HSO4- ion is made from H2SO4.
Since H2SO4 is a strong acid, HSO4- would be further ionized in water to give H+(aq) and SO42-(aq).
HSO4-(aq) → H+(aq) + SO42-(aq)

(2) Consider NaHCO3.
Since H2CO3 is a very weak acid, HCO3- has a weak tendency to further ionized in water to give H+(aq) and CO32-(aq), but has a stronger tendency to hydrolyze in water to give back H2CO3(aq) and OH-(aq).
HCO3-(aq) = H+(aq) + CO32-(aq) [weaker tendency]
HCO3-(aq) + H2O(l) = OH-(aq) + H2CO3(aq) [stronger tendency]
(‘=’ represents double arrow to show reversible reaction.)