How do I get values from a one2many field?

Question

I have three models which are connected with each other. The first one is an inheriting of product.template (product_template.py) and as you see I have a one2many field which is connected to the second model showed in here.

When I want to access variables from product_template.py with dot notation I can see variable suggestion and I guess it works fine.

class ProductTemplate(models.Model):
    _inherit = "product.template"

    kestet_ids = fields.One2many('kestet.lines', 'product_template_id', string="Kestet", store=True)

class OnetoMany(models.Model):
    _name = "kestet.lines"

    partner_id = fields.Many2one("res.partner")
    kestet = fields.Char(string="Emri i Kestit(n)")
    vlera = fields.Integer(string="Vlera e Kestit(n)")
    data = fields.Date()
    sel1 = fields.Selection(
        [('kontrate', 'Kontrate'), ('levrim', 'Levrim Kredie'), ('karabina', 'Karabina'), ('hipoteka', 'Hipoteka'),
         ('Celsat', 'Celsat'), ('Ne Perfundim', 'Ne Perfundim'),
         ('other', 'Tjeter')], string="Menyra Likujdimit")

    pagesa1 = fields.Selection([('Cash', 'Cash'), ('Bank', 'Bank'), ('Klering', 'Klering')], string="Menyra Pageses")
    product_template_id = fields.Many2one("product.template")
    property_contract_id = fields.Many2one("property.contract")

Now when I try to access it from this other model property_contract.py and do the same thing as above, it doesn't give me variable suggestions and I can not access variable values.

class PropertyContract(models.Model):
    _name = "property.contract"
    _order = 'start_date'

    name = fields.Char("Contract Number")
    kestet2_ids = fields.Many2one('kestet.lines')

I also tried:

installment_id = fields.Many2one("product.templates")
installment_relation = fields.One2many(related="installment_id.kestet_ids")

It failed giving me results. I tried also the above code but didn't work...

What am I doing wrong here?