I am really new to parrots , but I did some research saying cockatiel are easy to tame but some don't but ,so... I bought a pair from a petshop, and I know I could be dumb but... I forgot how old they are....so I'm sorry

but the petshop owner said they were raised by their bird parents.....so hope it could help me with this problems...
But I got individual problem each of them and a problem as them together...
Female Cockatiel problem:
the 1st day and 2nd day where kinda tough , cause she wouldn't eat from my palm , and even afraid of millet so I always catch her wings and neck to bring her out the cage and tame her , but what is weird is she is so behaved in the stand but would somehow run to the edge opposite of mine, but here comes 3rd day , as usualy she bites when i try to get her out but it doesn't hurt much , so i teach her step up , and she can , and she even wouldn't fly away if i put her in my shoulder and bring her to bigger room , but as immediately seeing the cage , she would try to fly to the cage

so i run to the bathroom before she could , so i continued , she doesn't bite me when I try to pat her in the head but if she had enough she would hiss or let her head lower away from my hand and open the beak a little , so I know , and she isn't afraid of eating from my hand also which is wow for me , and even drank the water i have in my palm.... but as soon as I put her back to the cage , she would start running away from my hand again just like usual like I am a total stranger:( why is her attitude different from the cage from the stand.....
male cockatiel problem:
from 1st to 3rd day which is today.... I never made progress as much as to the female.... he would ALWAYS bite my fingers hard...my poor fingers

so red....so whenever i am training him , he would run away , and go to a corner or if there is something in his way, he would bite it so hard and even he is in the stand , since the stand is made up of small branch and tied with copper wire in the middle, he would go there and bite it and the small branch is really pilled off... I can see he really bite so hard... which at this moment I am afraid what to do anymore, and when he runs away , and when I try to use a perch to put him back to the stand , he wouldn't budge an inch or what, and even bite the perch hard , and would back off a little , i tried using millet to lure it to the perch but it took me a long long while to bring him back even I let him calm down for few minutes before doing that....and whenever I have him in the perch and goona train him to step up in my gloved up fingers so his bite won't hurt , he would open his wings and ready to fly back to the stand and when I try to pat it , he bites, even i use distractions ,it doesnt help.... even i do it slowly like from his comfort zone and give him treat and near a bit and treat still won't work , after taking treats from me he would face my other finger that is ready to pat his back

please help I am really getting tired..... he is so different from the female

but i wont give up

just give me tips what to do....
when they are together problem:
so they live inside same cage, which is somehow small , but I am trying to make a cage that is double it , but for now , whenever I put them in 1 stand since that is the only one I have made , the female would bite the male when the male bites the copper wire. sometimes when they are inside the cage, both of them would bite each other , is this normal between them? please help
sorry for all the question... cause I don't know what to do anymore
oh by the way ,I move their cage whenever I will start training them so they won't fly away, but it is just a short distance dunno if that has something to do with it.....and if there is something you dont understand please tell me, cause I really need all the help I could help
