Pleasure Gael. If the changes are independent means one branch change won't create conflict with other branch change. So You can merge it with main branch in any order.

But if one branch change and other branch change has some common UI, Workflows, data-types, plugins anything means there is potential of conflict and in that case, You need to decide hierarchy of merge and merge in sequence of that hierarchy. On each merge, testing of overlapping areas must be done.