If he had any smarts at all, Tommy would be fighting to get the baby placed elsewhere - working with another different lawyer for the baby - to keep the baby out of a prison where drugs, open sex, overcrowding, rapists, child sex offenders, and other criminals are rife.
It wouldnt take long for the other prisoners to realise that Heather is a self-absorbed nut case and support him imo.
And if he were
really smart, he would realise that to follow the money (sorry, Sheila

) he will need to follow the baby, get some kind of custody of her, look out for her best interests, get his family to care for the baby
or pay a local woman a pittance from the babys potential inheritance to wet-nurse and care for the baby, let her play in the sunshine with other children, and perhaps bring her for visits.
If he arranged all of that - via a lawyer for the baby - he could keep Heather locked up in prison for a long, long time
paying for the crime that she involved him in, and away from the babys inheritance. If he thinks Heather will keep him around for very long he is as crazy as her
she is 18, selfish and violent
shell kick him to the kerb sooner or later
probably as soon as she has completely used him to absolve her of any blame for Sheilas death.