My 124 and my 210 are/were only "emergency" transport for my 3 kids. The one in the middle always gets short shrift, which won't hold up for much more than an hour. BTW, sticking 3 kids in a W201 backseat probably qualifies as child abuse in the US
.
My recommendation is a minivan (preferably used) for the wife and kids, and you drive the MB.