A splitter will work as long as your signal is strong enough. Be aware there are 2 types of 3-way splitters. Some are unequal, with one output at -3.5dB, and the other two at -7dB (signal loss.) Others are balanced with all 3 having the same -5.5dB loss.
Another issue could be remotes. Most Comcast boxes use the same remote codes, so trying to control all 3 could be confusing unless all 3 are using RF mode. Depending on the remote, you may need to cover up the IR sensor on the box or the front of the remote to prevent the IR from controlling all 3 simultaneously.