Traveling with my English DH to USA for the first time... Immigration question

My DH said we have to go in separate lines when we get to the USA for immigration and we cannot go together since he isn't an american. Is this true or can he go with me to the citizen line?

Likewise going back to England can I go in the UK line with DH?

You need to ask when you get there.  They have always let us go together, but sometimes they want you to go through some lines and sometimes others.

We've (me - USC DH - UKC) always gone through Chicago and been told to go to the US Citizen line (we always forget and try to go through the non-citizen line and then are told to go to the citizen line)

If you get in the wrong line, all they will do is direct you to the correct one.

My situation isn't completely similar, but I was under the assumption that if you're in a legally recognized marriage you can go through the line together in the US and the UK.  However, because I"m in a civil partnership, which as you know isn't recognized by US Immigration as a legal partnership, we had to go through separate lines and had to fill out individual landing cards.  It felt rather odd putting "0" in the section asking for number of family members travelling with me .  BUT on the way back to Belfast, we went through the UK/EU line together and were waved on through by the IO.   

As others said, ask when you get there. I'm UK citizen, my wife is American. We've been over twice since we got married, asked the guy at the line and both times went through together. First time in the US line and the 2nd time in the Green card line. They prefer you to go through together, and your husband will find it's so much easier, far less questions asked as to purpose of visit etc.
Coming back into the UK, again ask but we come back in the non-EU line because the line is shorter! Brilliant, both ways now we usually get the short line.
Next week we are going on holiday to Greece, coming back I know we'll come through an empty non-EU line! 

Has anyone travelled with their in-laws?  DH, his parents, and I are planning a trip to the US this autumn.  Do you think that we'll be able to stay together or will DH and I go through one line while his parents go through another?

You are one family - you can go in the same line together...and I've always gone in the US line going into the US and UK line going into the UK (even with inlaws).