Can people be redeemed two or more times? The Israelites were first redeemed from Egypt bondage and again when Christ died for Israel (Galatians 4:5; Hebrews 9:15). Did Jesus's death on the cross redeem the Jews (a third time) as well as the Gentiles, 1Timothy 2:6?

As for the Jews who were in Egyptian bondage, when their foretold time in Egypt passed (Genesis 15:13), God led them out from Egypt (Genesis 3:17), but did not redeem them from the Adamic death sentence. To speak about redemption, there must be two participants – seller and buyer. In Egypt, no one paid Pharaoh for the Jews. 

Consider the totality of Jesus’ redeeming sacrifice in 2 Timothy. 2:3-6, “…God our Savior, who desires all men to be saved and to come to the knowledge of the truth. For there is one God and one Mediator between God and men, the Man Christ Jesus, who gave Himself a ransom for all, to be testified in due time.” These verses teach that God had a great desire for  all people (who have ever lived on earth – including the Jews) to be redeemed from the death sentence. Furthermore, God’s intention was realized in the form of Jesus Christ.  As a perfect man, Jesus redeemed Adam (and all mankind yet to be born). Jesus died in order to take Adam’s death penalty upon Himself. He thus freed Adam (and all his posterity both Jews and Gentiles) from the grave. Then He sat down on the right hand of God. (Hebrews 10:12)

Respecting Galatians 4:4,5, “God sent forth His Son, born of a woman, born under the law, to redeem those who were under the law…”, the Jews were additionally condemned because they had made a covenant with God to keep His Law. The Bible declares they were unable to keep their promise. However, when Jesus was born a Jew (under the Law) and then died having kept the Law perfectly, He removed that condemnation at the same time.

Specifically: For whom was Jesus the ransom?
“…in Adam all die, even so in Christ shall all be made alive.” 1 Corinthians 15:22
“For as by one man's [Adam] disobedience many were made sinners, so by the obedience of one [Jesus] shall many be made righteous.” Romans 5:19

Was Jesus’ sacrifice sufficient to redeem mankind or are further redemptions necessary? Hebrews 10:10, “…we are sanctified through the offering of the body of Jesus Christ once for all.” Jesus redeemed people once for ever by his one sacrifice.