Using SSH to clone upstream into project bitbucket server

[HalHockersmith]

I am trying to setup bitbucket server to help coordinate change tracking and ticket fixes as implement changes on a rewrite of our software. I have Jira running so I wanted to be able to use the "start branch from ticket" feature with bitbucket server. The challenge i am running into is that our upstream provider we license some of the code from uses SSH with public keys ONLY for access to the code. I am trying to figure out how to clone from them so I can use fork syncing.

Is there a way to use SSH to clone/sync an upstream repo?

Or do I need to create a new repo, push code from our current clone, and then setup the remote somehow with the other team to access it?

Here is the diagram of what I am trying to do. Any ideas here would be nice. Thanks.

Dev 1 ------\
Dev 2 -------|---- [HTTPS] ---- Bitbucket Server ---- [SSH] ----- Upstream provider
Dev 3 ------/