1. I like her who has been with Tom.
2. I like it that belongs to Tom.
3. She who is smart and brilliant is going to meet with them tomorrow.
4. They who didn't wash hands before meals are to get infected.
Are these sentences grammatical?
1, 2 & 4 aren't. 3 may be grammatical, but it's unnatural. Generally, relative clauses aren't used to define pronouns: use a noun: for example 'I like the woman who was with Tom last night' .
I'm in doubt about 3, because it's structurally adimilar to the usual translation of Morituri te salutant - 'We who are about to die salute you' (English doesn't have a future participle, so we use an indicative instead.)