bad dog?

Posting anonymously for fear of people losing their minds over this post. 
Hubby and I have a 9-year-old rescue that we've had for a year. 12-pound Boston terrier-chihuahua mix. He is sweet, but NEEDS. HIS. SPACE. He bit our three year old nephew because he got too close.  He's bitten me for touching him when he didn't like it. He is very noisy, too (barks nonstop when hungry). He has some warts that make him not a "cute" dog, and is aging so I'm sure he'll have more problems.  The no-kill rescue we got him from said they would take him back, but I don't think anyone will ever adopt him since he's not cute, is getting older, and has a history of biting. I'm a FTM due in February, and I just don't want to have to worry about my dog biting my baby. He can't be trusted. I also don't want my son growing up afraid of dogs because we won't be able to let him near this dog. What should I do???
Update with further details: husband and I both work 12 hour days, which will continue after I return from maternity leave.  Additionally, we do not have the financial resources to afford training and long-term medications for the dog.