Are they within the carry-on luggage size (10 x 16 x 24)?
Also, you are limited to one carry-on and one personal item (like a briefcase or purse), so you cannot add these paintings as carry-on. But you could substitute for the bag if the dimensions are within guidelines and they are bound and packaged together as one item.
Lastly, if they are smaller than 30” by 17”, you could probably bundle them together and buy them an extra seat and buckle them in like a musical instrument. Definitely call customer service at 1-800-435-9792 and ask first before paying for their own ticket because I am not qualified to definitively answer the question.
