How to solve this?

does regular html <form> can handle <cfgrid> feature.?

No. As Adam has said, cfgrid must be within <cfform>. You may of course use the HTML format, as follows

<cfform format="html">

<cfgrid format="html"></cfgrid>

</cfform>

tabsTop.cfm <cfoutput> <form action="post" action="SQL/#submitPage[SelectedTab]#" > </cfoutput> tabsBtm.cfm <cfoutput> </form> </cfoutput>

The start tag <form> and closing tag </form> must be on the same cfm page. You may use cfinclude to include the page containing the start or end tag.

How Can I get <CFFORM> to make it work in this scenario and to use cfgrid?

The cfgrid documentation has an example you can run directly. It uses the datasource, cfdocexamples, which comes with Coldfusion.

<!--- Query the database to fill up the grid. --->
<cfquery name = "GetCourses" dataSource = "cfdocexamples">
    SELECT Course_ID, Dept_ID, CorNumber,
    CorName, CorLevel
    FROM CourseList
    ORDER by Dept_ID ASC, CorNumber ASC
</cfquery>

<h3>cfgrid Example 2</h3>
<i>Currently available courses</i>
<!--- cfgrid must be inside a cfform tag. --->
<cfform format="html">
    <cfgrid name = "FirstGrid" format="html"
        height="320" width="580"
        font="Tahoma" fontsize="12"
        query = "GetCourses">
    </cfgrid>
</cfform>

You're going to need to revise your logic so that your <cfform> tags are within the same file.  CFML needs to be compiled before it's executed, so the CFML wihtin each file needs to be syntactically complete; one cannot rely on possible runtime considerations (like which files get included) during the compilation phase of proceedings.

And, as you suspect, <cfgrid> controls need to be within <cfform> tags.

The best way to answer questions like this is to give it a try and see what happens.  CF will not bite you if you get something wrong, so there's little risk in having a mess around with stuff.  It's a good way to learn.

--

Adam