They might have had kekkei genkai abilities just like we see with hashirama but because we don't have enough information about them, we shouldn't assume they didn't have kekkei genkai abilities.
You do realise the senju and their closely related descendants were gifted with the only bodies that were capable of handling the optical kekkei genkai, that is the sharigan and the rinnegan(nagato) so they were blessed with this instead. Plus they were too strong, they didn't really require kekkei genkai
N hashirama isn't the one one who could use wood style, yamato too can perform wood style jutsus.