My view is at this age you just do what you can do when you can do it, don't make it a fight, if they get a bit of toothpaste in their mouth somehow or another, job is a goodun.
I found variations of the following works:
me + toddler cleaning teeth opposite each other,
letting toddler clean my teeth, then I have a turn and do their
letting "toys" clean their teeth (you hold toothbrush in the hand of the toy),
letting DD clean DS teeth,
pretending you've spotted something and you need to brush it away (i pretend i spot all sort of silly things in there and "quick let me brush it away" so it's a game)
standing in front of a mirror
give them toothbrush + paste in front of tv so they absentmindedly put it in their mouths for a bit
let them do it themselves and ask for 'a turn'