Does marrying seven months after the father's death, and the uncle refusing to attend before an Eid passes since the death, constitute severing ties of kinship?

There is no legal basis for what your uncle mentioned regarding the condition of an Eid passing after your father's death to complete the marriage. Therefore, there is no harm in you completing the marriage. If it is easy to convince the uncle, that is preferable, but completing the marriage without his consent is not considered a severance of kinship ties. We advise you to strive to convince him and seek help from those you trust.