What is the ruling on seminal emission during sleep on Ramadan nights if ghusl (ritual bath) is not possible due to the lack of a designated place for it in the house?

If by "emission during sleep" you mean a wet dream, then it does not affect the fast whether it occurs at night or during the day. As for not performing ghusl (ritual bath), the absence of a designated place for ghusl at home is not an excuse to abandon it. Rather, you can perform ghusl in the mosque facilities, for example. If it is completely impossible to find a place for ghusl, then you are permitted to perform tayammum (dry ablution).