Does The Devil and His Demons attend people funerals?

 no they only exist within the religious mindset im afraid

If by demons you mean misshapen monsters created by Satan, there are none.  There are only the evil spirits who "kept not their first estate," unlike us.

I don't think they bother with funerals.  They're too busy out tempting us to get into trouble and unhappiness.

I have a friend who's a funeral director.  As such, he sees a wide variety of faith and non-faith funerals.  But the most disturbing funeral he ever directed was for an avowed atheist.  He could not just sense, but feel the evil pervasive in the room.

Most people have 'familiar spirits' assigned to their family and lineage, so they come along for the ride with their 'surrogate' wherever they go and thrive on sadness and misery. Jesus called those who focus upon the supposed importance of funerals, "The dead burying their dead." (Matthew 8:21-22). 

Demons are arranged into hierarchies which human power structures have come to resemble, so the devil and his arch demons seek to influence human power structures, social movements and entire populations at geopolitical levels, while demons of lower rank inspire and influence population segments all the way down to family levels and individuals, (i.e. 'familiar spirits').  

Demons have no respect for God nor His creatures so I assume not.