To stop the charges for load balancing, you need to delete the forwarding rules and/or delete the load balancers themselves.
Remember, Google Cloud charges for forwarding rules whether they are created for load balancing, and for most load balancing use cases, you need only one forwarding rule per load balancer.
I might consider the low cost vs delete the load balancing:
The following examples use US pricing:
For example, if you create one forwarding rule, you are charged $0.025/hour. Entire weekend =0.025 x 64 hours = 1.6 USD
(Just for forwarding rules, it suppose no traffic because you have the VM instance stopped).
It is on the GCP's documentation