How can we as grandparents stay legally involved in our granddaughter's life in Oklahoma?

Our son and our ex-daughter in-law have had a recent situation come up that is sending our ex d-in-law to her lawyer to file full custody of our granddaugher. What direction should/can we take in order to remain actively involved in our gr'daugher's life here in Oklahoma? Our son has the option of supervised weekly visits in the ex's home but isn't happy with that arrangement. Our son is a full time college with a full time job. He cannot afford to go to court and plea his case. His lawyer states it could cost our son up to 10,000.00. Is there a better way for him to ask for joint custody which he does not have now? He has our granddaugher every other weekend and 2 half days throughout the week. Since this last situation, which was a wrongfully accused public drunk, his ex is asking for full custody. Our son will have to work out the details with his lawyer, but back to the original question, what do my husband and I have to do to remain in our precious and wonderful granddaughter's life?

Thank you so much for your help.

A scared grandma and grandpa.

Thank you for your help.

( :