If the reality is as you mentioned that you were involved in causing the death of two persons, you are obligated to
make Kaffarah for involuntary manslaughter for each victim. This Kaffarah is freeing a believing slave; but if this is beyond your means, you should observe Sawm for two consecutive months. Nothing else will be enough to expiate for this. This is because Allah (Glorified be He) says:
It is not for a believer to kill a believer except (that it be) by mistake; and whosoever kills a believer by mistake, (it is ordained that) he must set free a believing slave
until the Ayah (Qur'anic verse):
And whoso finds this (the penance of freeing a slave) beyond his means, he must fast for two consecutive months in order to seek repentance from Allâh. And Allâh is Ever All-Knowing, All-Wise.
Being a partner in the crime has no effect on the obligation of making Kaffarah by each partner. There is no harm if you take a rest after observing Sawm for two consecutive months, which is the Kaffarah for one victim, after which you can begin to observe Sawm for another two consecutive months to make the Kaffarah for the other victim. (Part No. 21; Page No. 270) May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.