Multiple branch rebase to a dedicated branch. Checkout the target branch and use the script.

multiple-branch-rebase.sh

#!/bin/bash

# checkout the target branch
# ./multiple-branch-rebase.sh <branch1> <branch2> ...

set -e

TARGET_BRANCH=$(git rev-parse --abbrev-ref HEAD)

for BRANCH in "$@"; do
    git checkout $BRANCH
    git rebase -i $TARGET_BRANCH
    git push -f
    git checkout $TARGET_BRANCH
    git merge --no-edit --no-ff $BRANCH
done