Is it permissible to sell televisions and video players, which often display what is forbidden or doubtful, in order to pay for mosque land or to help build it, and to whom should these devices be sold?

Do not sell entertainment instruments, because most of those who buy them use them in unlawful ways. It is better to destroy them to get rid of evil, and you will be rewarded for that. If you find someone who you strongly believe will use them in permissible ways, then there is no harm in selling them to him.