Their display guidelines differ slightly but both state that you cannot alter or modify any content displayed from their networks.
Note, if you alter or modify the content you run the risk of being contacted by the respective sites and being asked to update your posts as per the following guidelines.
To review the Instagram guidelines please click on the following link - https://instagram-brand.com/guidelines/general
To review the Twitter guidelines please click on the following link - https://dev.twitter.com/terms/display-requirements
If you do wish to alter the post information then you will need to get the Rights from the content creator to do this. Find info on Rights Management here.