W4 question

My husband is working and we have 3 kids he claimed 3 dependents on his w4 we noticed he’s not getting any federal taxes taken out. ( this is a new job)  did he make a mistake? We double checked and he’s not claiming exempt so I’m not sure what’s going on. 

I also just started working a part time job. I made the mistake of also claiming 3 ( I didn’t realize the higher paying job claims the most deductions) well same thing I got no federal tax taken out of my check.  

help! I’m really confused on the w4 break down. Should I be claiming zero since my job is making less? Should he change his deductions to get federal  taken out? Will we owe at the end of the year? Has something changed with the federal tax with holdings we’ve always had federal taken out. FYI we make less then 50 thousand a year and qualify for child tax credits. 

I just want to make sure we don’t end up owing at the end of the year. Thanks  please help