Dog owner question

Hello everyone!! I have a question. So we have a 2 year old bullmastiff. 
A friend of ours passed away so we will be taking in his dog for 6-12 months until our other friend(  his gf ) can find a pet friendly place she can afford. His dog is a 4 year old pitbull. (They have a 3 year old together and this dog is her best friend. He was going to be dropped
Off at the shelter and I didn't want that to happen)
Him and Rhea are roughly the same size (around 80 lbs). 
They have met TONS of times before. They seem to really love each other on smaller visits. But around a year ago we watched him for a week while they were on vacation and by the end of the week I saw my dog getting a bit nippy toward him. I think it's jealously. 
I did notice he was the dominant one over her, and she is naturally a very dominant dog so I was surprised. 
Do I still need to do a neutral introduction with them when he comes to live with us? These two have played before tons in each other's yards and houses
Since my mastiff was a puppy. 
Also does anyone have any tips to make this go smoothly?