Is it legal to write emails pretending to be someone else

my childs grandfather made up an email account for him and his son to communicate with me regarding our daughter. the grandfather and father THINKS that i have no clue about this, although i have called them out on it…but got no response back about it. BOTH write emails to me…but grandfather writes emails as though it were the father doing the actual writing of the emails… father has a learning disability, types COMPLETELY different than his father does…so its very obvious that 2 ppl are writing these emails, BUT making it look as though its just me and the father are the only ones communicating. is this legal??? father misspells words badly, doesnt use proper grammar, doesnt capitalize, keeps things short and to the point. example…father will write u need to corrected this…grandfather writes LONG paragraphs, addresses emails as hey (then my name) then ends email with Thanks (then the fathers name), grandfather also uses … (dot dot dot) in his emails, grandfather also capitalizes, grandfather also types very intellectually…with an occassional misspelling of words…im assuming to attempt to throw me off. its very obvious that its 2 different ppl writing me emails…is this legal for the grandfather to pretend to be his son emailing me??

This really isn’t a family law question, but if he has his son’s permission to send the emails then I can’t imagine this would be a problem.