Is it possible to go up to 4th jhana while maintaining awareness of breathing?
It depends upon what you mean by "maintaining awareness of breathing." The point here is by the time we get to the 2nd jhana the meditation technique becomes irrelevant and we have to dump the technique in favor of a still mind. Nonetheless, in the case of observation of the breath, the breath remains with us until we go out of body in the 5th stage of ecstasy, but from the second jhana on it is better described as bare attention. And, arguably, the 4th jhana is nearly an OOBE where we still believe we are in the physical body, but it doesn't hold, or demand our attention. The level of body awareness at the 4th jhana is minimal which explains why those who are at the 4th jhana do not feal pain, or the effects of gravity.