I'm doing taxes online and would like to change my status to mfs from mfj with my husband, but I have already started it online but not finalized it. Can I change it now and him claim our 3 kids and file mine when I receive it later?

If you have NOT YET filed the return, you should be able to change your status.

If the on-line tax software will not allow it, DELETE what you have done and start over.