How to implement Ad Hoc on Radio Frequency node?
A very simple protocol you can implement will consist of following things 


Dedicated Transmitter-Receiver pairs: 
Things will get simple if you assign specific responsibility to each node. This responsibility is to take data from the previous node and ensuring its successful delivery to the next node. (and thus obviously discarding any other data from any other node)
Use of acknowledgment(ACK) to ensure successful delivery of the data:
If a transmitter(let's say rep 2) sends data to its intended receiver (rep 3 in case of rep 2 as transmitter), then the receiver (rep 3) should send an ACK signal back to the transmitter(rep 2) to let it (rep 2) know that the data has been received correctly. Thus transmitter node (rep 2) will not reattempt retransmission. 
Avoiding resending the data which has already been passed to the next node:
Assigning sequence number (or packet number) to each newly generated data packet will help to discard any previous data which has already been taken care of.
Structuring the protocol/algorithm in such a way that the nodes cause minimum interference to each other:
you can implement schemes such as slotted ALOHA, random backoff, CSMA-CA. Although some of these might not be very necessary depending on your scenario (e.g. If your wireless network is expected to carry huge data, then you will have to take care of proper scheduling of the data and avoid collisions. In that case above schemes will be very helpful).


Also, understand that there is always a trade-off between data rate and range you can get. If your wireless link between end nodes (Tx node and Rx node) is expected to carry only small amount of data, then you can operate at lower data rate which will result in high sensitivity improvement and thus range improvement, in that case repeater nodes might not be necessary. Si4432 is 900 MHz transceiver and these RF frequencies have quite high penetration in the air, in the order of few kilometers depending on how you design your wireless link (keeping low data rate, using directional antennas, proper modulation protocol etc).