"活动议案通过者" can be translated as "those who have approved the activity proposal" or more concisely as "approvers of the activity proposal".
If you want to emphasize the role or status of these individuals in the context of the activity, you could also say "the individuals/participants who voted in favor of the activity proposal" or "the supporters/backers of the activity proposal who facilitated its passage".
However, for a straightforward and commonly used expression, "approvers of the activity proposal" would be a good choice.