What is the ruling on allowing Christians to upload videos of their religious beliefs without disparaging Islam on a public website, and likewise, what is the ruling on allowing "innovators" to upload videos of their beliefs as long as they do not infringe upon the symbols of Islam?

The website you own must not permit the publication of falsehoods, such as discussions by Christians about their religion, because these propagate falsehood and invite people to it. Everything other than Islam is false, as Allah the Almighty says: "And whoever desires a religion other other than Islam, it will never be accepted from him, and in the Hereafter he will be among the losers." The same applies to innovators (people of bid'ah); it is not permissible to publish their discussions that promote their falsehood. It is advisable to stipulate the prohibition of publishing anything that contradicts Islam and the creed of Ahlus-Sunnah (the People of the Sunnah).