I appreciate what you're saying - I was Chair of our school PTA for three years. It's hard because there are so few of you. If you leave then there will only be three members. Is it just the four of you doing the work? That's not how it should be. We started with three members who took handover from the outgoing parents and we quickly recruited as you can't do it with just three people.
I would suggest recruiting class reps. One from each class would be great, two would be amazing.
Class reps could spread messages about events via class WhatsApp groups and recruit helpers for big events.
You also need to find a way to cut down comms so your WhatsApp isn't blowing up every day, but you still need to be able to give information about events, organising helpers etc. Some groups can be set so that replies are not possible - so you could do a PTA group msg with event title and details and then "meeting for X event in local pub on X date".
What did our parents do before WhatsApp? They signed up then turned up. They had in-person meetings to plan events, then they followed up on actions.
WhatsApp now seems to be a way for people to go "yeah I'll help" and then after 100s of messages flying about is swiftly followed by "I'm dropping out because excuses".
It isn't an easy task being on the PTA. People love to slag it off as being cliquey but they don't see the half of what goes into organising stuff - they see "the same people" doing everything and assume it's a clique. It not! It's because nobody else steps in to help, or people offer and then pull out last minute so it falls back on the core team to take on more tasks.
I was lucky as Chair, we had a fantastic team who all pulled together to run events. It was the most successful PTA the school has ever had and we still laugh about some of the behind-the-scenes antics now. Every one of us had a job and children but we made it work. We were also lucky to have a group of helpful dads so it didn't just feel like more work for mums!
Good luck - have a chat with your other members about spreading the load and being more efficient with comms.