If you are using voice grade radio communication equipments such as those walkie talkie with only mic jack and speaker jack. You can try the packet radio methods used in the ham world. Since direct FSK method requires the frequency keying input of the radio equipments, so if only audio input/output , you need to key a audio tone instead of keying the RF directly.
Try to search the google with the key word "packet radio" or "tnc" or "AFSK modem" ...etc.

I had ever used the very old method of the XR2206/XR2211 many years ago. However you need to trim and tune the circuit and that is not good. In the mid 90's, some TNCs used the TCM3105 modem chip (Bell 202 or something like that, forget).. You can try to check if we still got this good chip in the world or not..

Okay if you solve the radio interface problem, you need to solve the problem of the protocol.. The ham packet radio uses AX25 protocol which is similar to HDLC (many TNCs used the Z80-SCC at that time to implement the protocol). This protocol is not that easy to implement purly in software anyway.

Well if it is a school project, my suggestion to you is using simple protocol with the most essentials data in the frame only.....

Good lucks..
Best 73 from Li.