Answered by: Mufti Maruf Ahmed
I know that if we see our Prophet peace be upon him in a dream, then we have certainly seen him, as the shaitan cannot take his form. But do we have any knowledge about whether this also applies to the rest of the prophets (peace be upon them)? For example, if one sees (or thinks he sees) the Prophet Musa alayhis salam in his dream, then has he certainly seen Musa alayhis salam without a doubt, or is there a possibility that he only saw the shaitan taking Musa alayhis salam’s form?
In the name of Allah, the Most Gracious, the Most Merciful
There is no doubt that whoever sees Prophet Muhammad (Sallallahu Alayhi Wa Sallam) in their dreams has indeed seen him, as Shaytan cannot take his form.
The Prophet (Sallallahu Alayhi Wa Sallam) said: “Whoever sees me in a dream has really seen me, for Shaytan cannot take my form.” 
As for seeing other prophets in dreams; according to most scholars, Shaytan cannot take their forms either.
Imam Al-Baghawi (rahimahullah) writes: “Whoever sees the Prophet (Sallallahu Alayhi Wa Sallam) has actually seen him, as Shaytan cannot take his form. The same applies to all other prophets as well as the angels (peace be upon them all).”
Imam Al-Aini (rahimahullah) writes: “(Seeing ‘Isa (alaihis-salam)) is a true dream as Shaytan cannot take the form of the prophets.” 
Only Allah knows best
Written by Mufti Maruf Ahmed
Checked and approved by Mufti Mohammed Tosir Miah
Darul Ifta Birmingham