If Bluetooth and Wifi doesn't work in the same time, if you want to use a splitter/divider have to consider the +10dBm Bluetooth TX power going to the input of the Wifi receiver, and about +20dBm from the Wifi TX to the input of the Bluetooth receiver. In this situation the best is to use an antenna switch, which can be a simple diode that gives about 20dB isolation.
You cannot use a diplexer, because BT and Wifi have the same frequency range.
You can use split traces making an on-board splitter/divider, but again, have to take in considerations TX powers going to RX.