I don't know what plans Chelsea have for replacing Lukaku but Christiano Ronaldo moving to Chelsea seems very unlikely. He wouldn't do that to Manchester United.
Agree. Ronaldo isn't a typical player who is eager to move to the rival of his club in the same league. We must remember when there was a rumor that Man City wants to sign him, but he finally agreed to move to Man United then. If his priority is for the salary or the title, he must prefer moving to Man City. The great thing was that he prefer to return to Man United because he remembered Man United big role in his career. So, it is simply unlikely to happen moving to Chelsea.
Lewandoski might be open to a move to Chelsea and with his price tag Chelsea are in a better position to get him than Barcelona at the moment and I think he will be open to the idea of moving to the English premier league.
Chelsea is superior compared to Barcelona because they seem to have bigger funds. But don't forget that Real Madrid is also interested to sign him. I think Lewandowski prefers to move to Real Madrid if there is a serious offer. Real Madrid must have enough money for the expected price made by Bayern Munich. Real Madrid has no problem with financial strength, they have no bad rumors as well. In addition, Real Madrid is the king of UCL competition and the best team in La Liga, Lewandowski should consider these factors.