Marchesa vs grave betrayal

[Taysby]

the opponent to my right has out a spell that destroys all creatures. I have {marchesa of the black rose} and 2 other dudes out, all with +1+1 counters. The opponent to my left has {grave betrayal} out.

If I understand it correctly, my ability to return the dudes gets put on the stack first (apnap order) and then his goes on on top. His would resolve first saying at the next end step he will get them. They are still legal targets for marchesa though, so her ability resolves and replaces the grave trigger so I get my creatures, correct?

[Kaylesh]

the opponent to my right has out a spell that destroys all creatures. I have {marchesa of the black rose} and 2 other dudes out, all with +1+1 counters. The opponent to my left has {grave betrayal} out.

If I understand it correctly, my ability to return the dudes gets put on the stack first (apnap order) and then his goes on on top. His would resolve first saying at the next end step he will get them. They are still legal targets for marchesa though, so her ability resolves and replaces the grave trigger so I get my creatures, correct?

I'm afraid not.

Both abilities create a delayed trigger at the beginning of the next end step. These triggers, putting the creatures from the graveyard on the battlefield, will be put on the stack in apnap order, causing his to resolve before yours, returning your creatures to the field under his control.

603.7c: A delayed triggered ability that refers to a particular object still affects it even if the object changes characteristics. However, if that object is no longer in the zone it's expected to be in at the time the delayed triggered ability resolves, the ability won't affect it. (Note that if that object left that zone and then returned, it's a new object and thus won't be affected. See rule 400.7.)

Marchesa looks for the creatures in the graveyard, they aren't there when they'd return.

[Younghawk]

Wouldn't it be determined who gets it by priority then? If player a is clearing the board and player b have  {Grave Betrayal} out and then player c has  {Marchesa, the Black Rose} out wouldn't grave betrayal got on the stack first since player b would get priority first and then marchesa would got on the stack last making it last on first out ruling so marchesa effect would over rule grave betrayal? Though I could be wrong

[griffin131]

the opponent to my right has out a spell that destroys all creatures. I have {marchesa of the black rose} and 2 other dudes out, all with +1+1 counters. The opponent to my left has {grave betrayal} out.

If I understand it correctly, my ability to return the dudes gets put on the stack first (apnap order) and then his goes on on top. His would resolve first saying at the next end step he will get them. They are still legal targets for marchesa though, so her ability resolves and replaces the grave trigger so I get my creatures, correct?

They are not still legal targets for Marchesa. As soon as Grave Betrayal resolves the creatures are no longer in the graveyard so Marchesa's ability fizzles.

But yes, because of APNAP it is possible for Marchesa to resolve first in some situations (notably, if the player with Grave board wipes).

[Kaylesh]

the opponent to my right has out a spell that destroys all creatures. I have {marchesa of the black rose} and 2 other dudes out, all with +1+1 counters. The opponent to my left has {grave betrayal} out.

If I understand it correctly, my ability to return the dudes gets put on the stack first (apnap order) and then his goes on on top. His would resolve first saying at the next end step he will get them. They are still legal targets for marchesa though, so her ability resolves and replaces the grave trigger so I get my creatures, correct?

They are not still legal targets for Marchesa. As soon as Grave Betrayal resolves the creatures are no longer in the graveyard so Marchesa's ability fizzles.

But yes, because of APNAP it is possible for Marchesa to resolve first in some situations (notably, if the player with Grave board wipes).

You are correct, but do keep in mind it is not a problem of illegal targets. Marchesa's ability does not target, so it will work on creatures with shroud for instance.
As a creature dies with Marchesa & Betrayal on the field, both abilities will create a delayed trigger at the end step. Depending on turn order, one of these will return the creatures, then the other attempts to return them, but they are not where the ability expects them to be, so nothing happens.
You can compare it with the exile of Emmy with it's shuffle trigger on the stack. Emmy will not be shuffled in from exile, even though it was in the graveyard when the triggered ability goes off. {emrakul, the Aeons torn} for reference.