Welcome to the ODK forum, @Pere! We're glad you're here. When you get a chance, please introduce yourself on this forum thread. I'd also encourage you to add a real picture as your avatar because it helps build community!
The key is what links your data. Each data row in your general data will be a household. Each household has one or more members, so each row in your people data will have the unique ID of a household linking it to one of the rows in your general household data. This is a One-to-many data model in which an element of "household" may be linked to many elements of "individual", but a member of "individual" is linked to only one element of "household". You'll want to use a pivot table on the household data to summarize on the unique household identifier values. Then you can use something like a VLOOKUP to pull that summarized data (for example, count of members in each household) across and add it as additional columns in your household data table.