I'm not sure how you're trying to integrate the two formulas. Where you're trying to nest one formula into the other formula. Nesting IF statements in a single cell can get confusing fast, so just take your time and make sure the nesting is correct and count the parenthesis, open & closed. If it helps with complicated nested IF formulas, write out all the separate IF statements on paper then use that as a guide as you type the formula into Excel.
As for the Range question...
There might be a better way to do this, but you could incorporate OR and AND inside the IF formula. For example, =IF(OR(Step4!L15="NA",Step4!L16="NA",Step4!L17="NA ",Step4!L18="NA"),"NA",(whatever it is you want to do when *none* of these cells = "NA").
Substitute AND for OR if *all* the cells you're interested in need to meet the conditions.