I don't really think your parents have thought about this thoroughly enough. What they are proposing has many implications and does not come without strings attached both emotional and financial.
From seeing my BIL move back in with his parents to disasterous effect I might add (there was no discussion and no rules beforehand, they have all made MANY, MANY mistakes) I would suggest the following guidelines:-
Rules. VERY IMPORTANT. All parties must talk to each other openly long before the move happens and detailed discussions between the four of you need to take place. No "sort of talk" will do - it has to be proper discussion. If this does not happen there is no point in moving back in with them. There must be rules and an honest expectation of who does what, when and why. No rules will lead to anarchy in their house and a lot of upset for all concerned. They could well turn around and say, "their house, their rules. Tough if you don't like them".
How long will you be staying with them?. You do need a plan to move out and the sooner the better.
Money is important, will you be expected to pay them rent?. Has this been mentioned?. What about utility costs?. These will increase for them if you all move back in. How much would you contribute towards increased running costs?.
Mealtimes can be another bone of contention.
They may want to eat at different times to you, who will buy food and will you all be expcted to eat with them or separately. What if they buy foodstuffs you don't like?.
Privacy is another important aspect that needs to be considered. This will be at a premium for your family unit if you are staying with your parents. You may find it very difficult to maintain a satisfactory sex life living in the same house as your parents.
Do they have a second bathroom?. Separate bathrooms/toilets are a must.
How are your parents with your children?. Will they complain about their playing around, how would you feel about them openly telling them off for misbehaving, giving them sweets you may not want them to have?. What about your social life, would they want to babysit your children for the evening if the two of you were to go out for a meal?.
How does your H get along with your parents?. If relations are not good there is another potential cause for friction between parties. And you'll be in the middle.
Any unresolved issues you have between them and you as their daughter could well come to the fore if you move back in. You could well come to resent them and this is why open and honest communication must happen before and during your time there - and keep happening.
I realise you have no choice but if you can instead rent a place this may be better for you all rather than living with them under the same roof. If you already feel it is going to be tough as they are set in their ways I would not actually take them up on their offer but rent instead.