Would be amusing to see how Saber does in an eating contest with these guys. :P
Kidding aside from what I'm looking up on them, the Heavenly Kings pack enough strength and durability on them where Saber would be having quite a bit of trouble taking them out individually and any clean blow they deliver to her from an attack would cripple her greatly and maybe even be fatal. While she has a speed advantage over all four being capable of Mach 15 speeds, I don't think regular sword strikes are working on the Heavenly Kings meaning Excali-blasting would be Saber's only resort at taking them out individually once she gets enough distance from them.
Against all four, I think Saber may be screwed. The numbers game would work to the advantage of the Heavenly Kings as their combined use of melee and ranged attacks would prevent Saber from having any time to prep an Excali-blast and leave her on the defensive until she is eventually plowed down.