hashirama wouldnt attack with his own body. he would use his forest. sand clones wont effect him unless he engages it in taijutsu. hashirama hits a sand clone, gaara comes out and seals him and he seals a clone and hashirama pops out under him and kills him with mokuton or a kunai. his dad would stand no chance against hashirama.
why would gaara have to come out and seal him?,he can easily do it in the air,and gaara can simply bury him in the dessert. This isnt chess,they will both be attacking together,and hashi will have to get his wood through gaara's auto defenceand his sand armour to hit him,assuming gaara dosent stay in the air,and his dad's gold dust is abt 7 times stronger than gaara's sand,he copied the techs of shukaku's previous jin,which was his wife,he learnt third eye,gold dust wave and gold dust wall,he definately can fly and spam aattacks.
Gaara's sand wave wiped out a forest at 13,he should be able to atleast match hashi's forest in the dessert,that plus a gold dust wave which is 7 times stronger than gaara's sand together definately destroys any forest hashi can make,gaara's sensor sand works in the air and the ground,hashi can't hide anywhere. Sand gold dust hail also catches anyone trapped there.
Hashirama is at a higher risk of being caught with a sand clone feint from gaara in a dessert than him catching gaara and his dad with a wood clone.
The kazekages win mid diff.