You do not need a "collective equivalent", albeit is a conjunction that means although (Cambridge). So it is not a relative pronoun that would need agreement in person or number.
The word comes
From the Middle English expression al be it (that), itself shortened from althagh it be that (“although it be that”), and thus composed from al (“completely, entirely”) + be (3rd person singular present subjunctive of been (“to be”)) + it. (Wikipedia)
However, you are not the only person who thought that there should be such an agreement. Wikipedia notes that:
Rarely, albethey is used when the meaning is “despite (the multiple things) being” rather than “despite (the single thing) being”; this is nonstandard, based on a flawed interpretation of albeit.
The it in albeit is the dummy subject of be. I have tried to find a reference stating that, but I couldn't find one.