Hello Everyone
We are operating a small WISP. We been using static routing and we had no redundancy at all but after having some power failure at some of our sites now we want to have redundancy and load balancing.So my question is can we just use static routing with different costs value for redundancy or we have to use a routing protocol and if we use routing protocol we have some other connection with main router that we do not want to be changed is it gonna effect them too. I am attaching a picture of what I want all replies are appreciated.
I was thinking of using ospf if in any case we have to use it and we also want load balancing on our links in case one fails the other one does not have problems .

Without more details it's hard to give a more in depth recommendation other than if possible I prefer a dynamic protocol to solve these problems.

Static routes are not ideal even with different costs and scripts.

A dynamic protocol will only load balance when the routes are equal cost so keep that in mind if you want more than one path to be used at once.

Also, the link will need to fail entirely (or at least enough packet loss for the protocols adjacency to time out). Layer 3 protocols do not have SDN like features to steer traffic on metrics like round trip time, latency or congestion.