Your problem is contractual rather than technical to discuss here. Scope of suply and analysis terminal point need to be discussed within your company internally, and with the other company if accepted and found logical (you are probably looking for this logical side in the forum). If you ask me yes both are possible and I have done it many times.
Again stress analysis scope must be contractual, otherwise if something goes wrong you can not provide proper documentation to the court. Is this reasonable for your case?
For the stress analysis terminal point, you can either determine a location for the 3 directional stopper (some prefer full anchor) and do the analyses on your scope by adding a couple supports on the other side to watch the behaviour (stresses in the pipe, displacement under the same load cases, and forces on the supports) of the pipe to compare analyses results. If you search this forum you will find very good discussions on the setting of terminal point and supports types may be used, and what to compare.
If both parties agree on the second option, one company can do both side of analysis all together. But watch the code to be used for piping beyond your terminal point. You do not have ability to mix two different codes in a single analysis model.
Next time please search the forum for your question first. You will be surprised for the number of discussions on the same subject. So, you would not wait for the answers.
Hope it helps.
Ibrahim demir