**Actually they were not under the curse of death by applying the blood by faith, while they died due to unbelief.**
The plague against the firstborn would have only killed the firstborn of the Israelites, if they hadn’t placed blood on their doorways. The plague did kill all of the firstborn in the land of Egypt, man or beast, where the blood was not applied. Pharoah, and much of his army, must not have been firstborn.
Paul said the Israelites were baptized unto Moses in the cloud and in the sea. At the Red Sea they were told that they would finally be delivered from the curse of the Egyptians (for under their yoke it was death or slavery, there was no promise of a new life):
“And Moses said unto the people, Fear ye not, stand still, and see the SALVATION of the Lord, which he will shew to you to day: for the Egyptians whom ye have seen to day, ye shall see them again no more for ever.” Ex14:13
Thus you nullify this from being typological of redemption by the blood of Chris if this salvation only applies to the first born children.
Paul said the Israelites were baptized unto Moses in the cloud and in the sea.
Which can represent both the baptism by the Spirit into the body of Christ (1Co. 12:13) and water baptism which confesses the Lord Jesus, signifying faith in Him. The issue is whether the act of baptism appropriates the washing of regeneration, or the faith that effects obedience, and whether souls can be thus washed before they are baptized.
It is clear that God purifies the heart by faith, and thus souls can be washed before they are baptized, but that faith that does not effect obedience, of which baptism normally is a part and the initial formal act, is not salvific.