Jarv was 9 1/2 when we introduced Jago - I think it was harder for him as we bought in a zoomy little boy who annoyed the hell out of him!
We didn't pander to Jarv's needs but we did allow him upstairs to have us to himself while Jago sleeps downstairs. We figured that that was his last bastion of having us to himself and Jago was so adaptable (and crate trained - he loved it, and we loved that he loved his crate
) that the separation at night was fine.
Apart from that life carried on - Jarv goes to work with my OH and Jago comes with me or to daycare. On walks they get on absolutely fine, and at night before bedtime both just curl up (separately but happily) where they like. They are very good at sharing - food, toys and us. I can honestly say there is never a cross word and both boys are entire.
My tip would be just carry on as normal - let them find their own levels and comfort zones. Sweep may love having company
The thing is that it will always take a while for the dust to settle but usually (especially with a boy and a girl) they will get on. Maybe at first feed them separately so there is no conflict about food, and if either of them resource guard (you usually) knock that on the head quickly.
It's a very different dynamic with 2 but lovely (I don't mind just having one though - this amazes people but Jarv was always the happiest only dog
)