It is impossible to say on Snowdon anything other than a few days in advance. At this time of year though you HAVE to plan for the worst. There is a very high chance it will have snow lying at the top and unless weather is settled then the risk of snow-rain-hail-hurricane winds-plagues of locusts etc is ever present in Winter. Unless your mates are experienced winter mountaineers then I would suggest they seriously consider giving it a miss until later in the year. There are plenty of lower level rides in the area which will be adventurous enough and are likely to be rideable in any weather. On the other hand it could just as likely be a calm sunny beautiful day with no snow and would be fine. But you cannot plan for that.
Having a go “because we drove all that way to do Snowdon, so we might as well risk it and see how it plans out” is generally a bad idea. Remember only a fool learns from his own mistakes…..