Greetings in that Divine and Most Precious Name of Our Lord and Savior Jesus Christ!
From my experience discussing matters of the Church with Sola Scripture Protestants I don't really think there can be any persuasive arguments, even if based upon Scripture, because in all honesty the entire philosophy of Sola Scripture is irreverent, illogical, and indignant. Folks don't necessarily believe in it because it makes sense so much as they have been persuaded by the misguiding (even if innocently) of others, and only God can persuade their hearts into the right direction. Further, many people project their own personal gripes and misunderstandings onto the Church itself and therefore reject it entirely and only come to Sola Scripture because from that ultra-Protestant ethos it becomes the only game in town.
Lets face it, in our Church we call these kinds of matters "Mysteries" precisely because we don't suppose them to be matters of intellect or mental comprehension or logic, rather they are actions of the Spirit of God in our midst. So we can not expect to explain away Sola Scripture to folks who adamantly believe in it, instead all we can do is continue in sincere and heartfelt prayer for them and be honest, compassionate, and humble when we share our lives with them. In this way, God will draw the back, just as He draws we Orthodox back in each process of Reconciliation/Confession and receiving Holy Communion.
This is not to say you shouldn't politely and respectfully discuss these matters and talk about the Scriptures with folks, including you in-laws, just don't be surprised if it takes a bit more spiritual patience and time for them to see the Light, which will knock them off their horse inevitably like it did Apostle Paul. Perfect typology, this story demonstrates the reality that only Paul heard the voice at the time, those with him did not comprehend what had happened and didn't receive the same Graceful vision. Perhaps they may have later, but our coming to Our Heavenly Father is mutually individual and communal.