All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.
Your claim that some Prophets will not get the Al-Firdaws is wrong. Al-Firdaws is the best part and the highest part of Paradise.
Al-Firdaws is a rank that the believers have been commanded to ask for. The Prophet, sallallaahu ‘alayhi wa sallam, said: “If you ask Allah, ask Him to grant you Al-Firdaws.” [Al-Bukhari]
The highest status in Al-Firdaws is Al-Waseelah, which will only be obtained by our Prophet, Muhammad
Therefore, Al-Firdaws has many ranks and levels; the highest of which is for the Prophet ; then the believers after him, each according to their deeds.
Faydh Al-Qadeer reads: “Al-Bukhaari and Muslim reported that the Prophet : “If you ask Allah, ask Him to grant you Al-Firdaws, for it is the best part and the highest part of Paradise.” The Throne of The Most Merciful is above Al-Firdaws.” [End of quote]
Therefore, reaching Al-Firdaws is possible for every believer. Allah would not make it permissible for us to ask for Al-Firdaws if it is a matter that is impossible for us to obtain. However, this is only possible to obtain by endeavoring in obeying Allah [performing acts of obedience] and doing one’s best in order to please Him, while always persisting in repenting to Him. This should be while one is relying on Allah and thinking good of Him, endeavoring in supplicating Him, and asking Him for that high status.
We ask Allah to bless us with Al-Firdaws and make us reach it with His Bounty and Favor. For more benefit, please refer to Fataawa 338950, 352693, and 339019.
Allah knows best.