I have 2 relatives with multiple ID's, do I just choose 1 to merge and ignore the rest? How do i then get rid of the blue box at the side of their name?
You will want to merge each of them, one by one.
Not sure what you mean about a blue box.
@Fiona Katrina Smith, you may want to start by reviewing, for each relative, each of the duplicate individuals (i.e., those that you find with multiple IDs). You will likely want to keep the individual's record which has the most complete or accurate information.
Once you've determined the individual's record that you want to keep then you'll want to determine what, if any, information you want to move from the duplicate record to the record that you've decided to keep.
To assist you, you may want to review the Help Center article, How do I decide if two records in Family Tree are about the same person? by clicking the title.
Hope this helps.