If their MAGI is 70K, then they are in the phase out. They can deduct 2,400 in a tIRA.
If they are in a situation where traditional is better than Roth, they should contribute $2,400 to traditional and deduct all of it, and $3,600 to a Roth.
If they are in a situation where Roth is better, then $6,000 to a Roth.
A backdoor Roth wouldn't apply here, so no reason to contribute any non-deductable money to a traditional IRA.