If you do a translation yourself and get it stampled by a notary, they might accept that! Worth a try since getting the notary to sign something should only cost a few euros.
Because your dh is registered for socio, yes you should be entitled to socio through his work as you are his dependents. Once you have your own ss card and number this would entitle you to medical treatment plus any benefits that are available to you including child ben, so yes you only have to do it once and it covers all these types of things. However I have been told that they only pay child ben up to 2 yrs old, but not sure if that's just our region (Murcia).
It is worth going to your hacienda and asking there, as all health centres, benefit offices etc seem to have different rules, as the legislation is constantly changing so not everyone has the latest version...aarghh! I assume you already have NIE and residencias if your dh is autonomo, but make sure also that ds has them (here it is now just one form and you can do both together at the police station, or same place you did your own).
It's a minefield isn't it, we still aren't sorted either and it's not through lack of trying! The bloomin rules change every other week, and by the time they give you the right forms they are out of date. AGH! That's why I'd suggest the hacienda, or if your budget can run to it have a word with a gestor who would be able to advise and then maybe just do the lot for you (for a fee of course!)
good luck, and if you find out, please will you tell me??!