1
I will go along with you.
Point to yourself for 'I', then use the 'ALONG' sign, moving your joined hands forward toward the person you are talking to. This shows you are accompanying them.
2
Can my dog come along?
Sign 'MY DOG', then use the 'ALONG' sign moving forward. Remember to raise your eyebrows and lean forward slightly while signing, since you are asking a yes/no question.
3
They came along with us.
Start the 'ALONG' sign slightly off to the side where 'they' are positioned in your signing space, and move your joined hands toward your body to show them accompanying you.