Is it permissible to say: O Allah, let us reach Ramadan neither losing anyone nor being lost?

The basic principle concerning supplication (Du'a') is its permissibility, so long as it does not involve sin or transgression. The supplication "O Allah, grant us to reach Ramadan, neither losing nor being lost" means not losing loved ones before Ramadan, and them not losing us. There is no harm in this, but it is better to omit it. Supplicating to reach Ramadan is permissible, but it is better to omit the addition of "neither losing nor being lost."