I grew up around Spanish and English. However, I was one of those kids who spoke "Spanglish" (neither good in Spanish nor English!). Anyway, I try to speak only Spanish to my grandparents (they only speak Spanish), my parents are bilingual,but mostly speak to me in English (unless they are yelling at me, they switch to Spanish...). But I switch my technology devices to Spanish, it forces me to figure it out since I need my cellphone and ipad. I put Spanish subtitles on my T.V., and watch my morning news in Spanish. I also mimic alot of what I watch, I listen to how the person talks and how they say it. Then I mimic how they say it, so that it's native sounding.

My fiance and I are both learning Spanish, but we don't do a good job talking as much as we should together in Spanish. It's more small talk then we go back to English.

Well, in my family we didn't use that , because only me and my brother speak English... Our parents speak only Ukrainian, so that's theoretically impossible to spend days speaking English.

But hopefully I can use this strategy with my kids(If I would have one), and I think it can help a lot.

It seems quite appealing to me that I can practice my target language with my family at home but it is a pity the primary language is more useful to exchange opinions in day-to-day life. Accordingly I basically do not think that manner can work well in my family.

However, the alternative option you may take into account is to arrange a period of time when all members in the family have to speak the target language and keep it on for a couple of months at least. The period of time in practice does not have to last for a long time each day and perhaps 30 minutes is quite enough if you keep on the practice persistently.