I've answered your first question earlier. If you search the commnunity, you can find it.
For the others, you can use the inbuilt custom validation.

https://community.qualtrics.com/XMcommunity/discussion/comment/53966#Comment_53966Thanks, Ahmed!
I saw the demo: https://iima.au1.qualtrics.com/jfe/preview/previewId/6caf466c-0db6-4964-a292-5ac372c61942/SV_4UvrcAjPQLSvewS?Q_CHL=preview&Q_SurveyVersionID=current
And this absolutely can work when I toggle Column 1, then 2 and 3 gets activated. I just don't know how to revise the code you created.

Qualtrics.SurveyEngine.addOnReady(function () {
    const quest = this;
    const qc = quest.questionContainer;


    const sbs_column_toggle = function (control_column, enable_option, target_column) {
        const control_options = qc.querySelectorAll(".Choice .SBS" + control_column);
        const enable_column = control_optionsoenable_option - 1].classList-1];


        disable_all(target_column);


        control_options.forEach((item) => {
            item.addEventListener(
                "click",
                (el) => {
                    let target_row;
                    el.target.ancestors().forEach((item) => {
                        if (item.classList.contains("Choice")) {
                            target_row = item;
                        }
                    });
                    const row_control = target_row.querySelector("." + enable_column);
                    const row_target_column = target_row.querySelectorAll(".SBS" + target_column);
                    setTimeout(() => {
                        if (!row_control.querySelector(".q-checked")) {
                            row_target_column.forEach((cell) => {
                                cell.disabled = true;
                                cell.style.opacity = "0.5";
                                cell.style.pointerEvents = "none";
                                cell.querySelectorAll(".q-checked").forEach((button) => button.classList.remove("q-checked"));
                            });
                        } else {
                            row_target_column.forEach((cell) => {
                                cell.disabled = false;
                                cell.style.opacity = "";
                                cell.style.pointerEvents = "";
                            });
                        }
                    }, 100);
                },
                false
            );
        });
    };


    const disable_all = function (target_column) {
        const all_inputs = qc.querySelectorAll(".Choice .SBS" + target_column);
        all_inputs.forEach((cell) => {
            cell.disabled = true;
            cell.style.opacity = "0.5";
            cell.style.pointerEvents = "none";
            cell.querySelectorAll(".q-checked").forEach((button) => button.classList.remove("q-checked"));
        });
    };


    sbs_column_toggle(3, 1, 4); // Selecting option 1 of column 3 enables column 4
    sbs_column_toggle(5, 1, 6); // Selecting option 1 of column 5 enables column 6
    sbs_column_toggle(3, 2, 2); // Selecting option 2 of column 3 enables column 2
});

You need to change the lines at the end to:
sbs_column_toggle(1, 1, 2);
sbs_column_toggle(1, 1, 3);

https://community.qualtrics.com/XMcommunity/discussion/comment/53992#Comment_53992This is much appreciated!

Hi, 

I have a similar dilemma. I have a side-by-side question where multiple choices can be selected, but I want to set a condition where the participant must select at least one answer per column. How do I do that, please? I have looked at custom validation but can’t work it out. 

Thanks

@ahmedA Thank you for posting this script; it’s been hugely helpful!

One piece I’m having trouble with:  In the control_column, I have multiple options that can be selected.   I modified the function calls to be: