You can cut as many scarfs as you need as long as they are in the correct supported locations. I once cut a 56' long plate with 16' timbers so we had to do several scarfs along that side.
There are other style scarf joints that are easier to cut and assemble. Which type depends on the forces on the timber. If it is a tension timber then one type is used. If there is low or no tension in the timber/frame then another can be used.
If it is a tie beam, then most likely there will be tension in the timber holding the two wall together. I would use a stop splayed tabled scarf with under squinted butts and wedges. This is a good joint for tension timbers.
Good luck with your projects
Jim Rogers