As MrsDragon says, it very much depends on which area of Germany.
We lived near Düsseldorf, where it was possible to rent a semi-detached house for around ?700 - 900 (plus water/electricity etc).
Other areas you could get a flat or house cheaper, but for 4 bedrooms you are going to be at least ?500. If you are going to Munich, at least ?1000.
You can apply for childrens allowance (Kindergeld) which is ?168 for first two children, then ?190 for third, which brings an extra ?558.
If only your DH works, then he will be in a tax bracket III, so will not be taxed much. I used this tax calculator and came to a monthly net salary of ?1868.00. That is after payment of tax, health, unemployment, pension contributions.
So you would have around ?2500. Which is an ok wage for Germany, but really very much depends on where you will be located.
Child care costs vary greatly. Where we lived the Kindergarten costs were adjusted so that those on lower wage paid less. And you only paid for the first child, the others were free.
You might get other benefits such as Wohngeld. I think that depends on where you live and how much your rent is. I would imagine that you would only get this if you were to live in an area where rents are high. I had a look at a program that works that out and reckon you might get another ?200 - but as I said, this very much depends on earnings and rent.
May I ask what your DH does? If you don't want to put it on here, PM me and I can give you a better idea if that is a normal wage for that job.