how to introduce 2 new kittens to and adult cat?

[Johnathon]

my uncle couldnt keep hes male and female kittens so i took them in. theyre in the garage and when i brought in my adult female immediatly the 2 females started hissing while the male just sat there. i put the adut back outside with some food for the night bc i didnt know if she would hurt the kittens or not. now i dont have a kennel or anything i can put them in so what should i do? i thought about just leaving the garage door cracked so if she did get mad the kittens could get out but theyre so new they might not come back. my adult really isnt aggressive at all so i dont get it. her whole life she lived with a cat but she passed a couple of months ago. what should i do so the kittens and adult will live together. NO COMMENTS ABOUT HOW CATS SHOULDNT BE OUTSIDE! CATS ARE PERFECTLY FINE OUTSIDE!

 

[Mindy]

Food is the answer with animals, get juice of tuna or some other canned fish and smear a bit on kittens....give adult cat just a taste of food and then put em all together.....leave them together...hissing is just a warning.
smear the juice on kittens every day and feed adult cat nothing but dry food sparingly...do not starve it just cut way down on normal amounts encouraging it to lick the kittens.
Also the adult will assert dormants by smacking them around a time or two but no blood.
This will have to happen for about two or three weeks before the adult accepts kittens as a normal co habitat.
good luck