A kingdom of honorable knights

>A kingdom of honorable knights.
>Except they are ghouls and eat evil beings in the name of their god.

Could they still be lawful good?

Yes

Kind of sounds like the broken lords.
Except the other way around. Previously chivalrous and just knights who now have to resort to feeding off innocents to stay alive.

>knigths fight evil
>knights eat evil
I don't see the problem.

It totally works. Alignments are what you want them to be. If in your setting undead aren't inherently evil or maybe there's a way to create neutral or even good undead, sure, you can do that.
Especially when they have a god which supports it, since that god is probably good and/or lawful as well

>Doomguy but hungrier and with actual morals

Yeah sure. Could be a covenant of redeemed undead or sumfin'.

They could definitely be good.
Lawful is a bit of a harder swing but still possible. If they have a strict code of chivalry then sure.

They have their bows.
Do they have a Good patron deity?
If yes, then yes. If no, then it may be debatable.

>lawful good means you must be good and lawful
That's not how it works and you know it

Good and bad all depend on culture and/or context.
If you want to make an action a good action, then go and justify it however you want.