Rav Hirsch points out that in Pesachim 90b it says that they had already undergone the Parah Adumah sprinkling (for the seventh day) and they were only waiting for sunset. Had they been allowed to join a group (that would be sacrificing) they could have eaten. however, that was not allowed.
One answer for Rabbi Akiva is that Nadav and Avihu died on the eighth of Nisan rather than the first (Rosh Chodes) as there is a machlokes as to when exactly the mishkan was first set up. One statement is that they started setting it up on Rosh Chodesh Nisan and יום השמיני was on the eighth day of Nisan. This meant that they would not have become tahor until after sunset and it would have been too late to be part of the korbon Pesach.
Others would say that the deaths were on the first of Nisan and one possibility is that the Parah Adumah was not yet ready and that caused the purification to be delayed.
A possibility for Rabbi Yosi Haglili is that they had to continue attending the coffin of Yosef while the mikdash was being set up and taken down (similar to the first answer) or that they might not have finished arranging for the Parah Adumah (as with the second possibility).
In either case, we see that there is an answer for both Rabbi Akiva and Rabbi Yosi Haglili.