Hi,
I believe the antenna splitter should work as expected in this case, you will not get such good quality as two separate antennas would give - but this solution will be better than having one antenna without a splitter attached.
The only recommendation I would give is to use antennas that are meant for the use-case with routers or modems, but if there's no possibility to get one like that - another kind of antenna of the same material should be alright.
EB.