How to get two dogs along ?

me and my nan haver had 1 dog for 9 years and we had a diffrent dog befor him and they got along ok . but she passed away my nan got a dog today and they are ok in the back garden but as soon as the new dog gose near him in the house all hell lets lose and i dno how to sort this out been told meany tip on how to do it but none off them work can u help me plz it doing my head in i dont want to igve away the other dog but im gunna have to if it gunna do that every timne they go near each other ?