How to do multiple user digital certificate signatures, first person works but second person has the option greyed out for them?

So we have a PDF that needs multiple signatures and information is added between each signee.  I digitally sign no problem then when I send it to the next person the option to digitally sign is greyed out.  We've made various attempts at the form in different situations but no luck.  Is there some trick in Adobe Acrobat Pro 2017 to allow each progressive person to add their e-signature to the document?