Both are correct and perfectly good English, but in both sentences, the middle section (rest in piece) should read: may he rest in peace: My grandfather, may he rest in peace, loved to watch/loved watching cartoons. That is how native speakers of English would say it, and there's no 'logical' explanation, except to say that is how we say it when we wish someone well, whether they be alive or dead, e.g. may you have a safe journey, may you soon recover, may her soul rest in peace, etc. It is the same as saying 'I hope you have/will a safe journey/will soon recover'.

Both are correct. Nevertheless, there is a difference between love/like +V+ing and love/like+to inf: Love/like+V+ing is used to express people enjoying the process of doing smth: I like playing the guitar (in general, always, I enjoy it ) Like/love+to inf, on the other hand, is used to express person's preferences (like +to inf=to prefer) I like to get to work a bit earlier than my colleagues She liked to wash the dishes right after the meals (both sentences are describing preferences in everyday life, routine and have little or nothing to do with enjoyment or excitement) I like speaking English (general feeling+ enjoyment) I like to speak English with our English-speaking partners (specific situation, preference)

You might also say "My grandfather, God rest him/his soul, loved...". I'm not so sure whether this is too old-fashioned, though.

They are both correct! The verb "love" can be followed either by a verb in the infinitive ("to watch") or one in the -ing form ("watching"). Hope that helps!!! :)

Both variants are great! Because the word loved frendly to either infinitive or gerund after it. To watch is infinitive form. Watching is gerund.